First, what is a CPaaS? Communication Platform as a Service is the expanded acronym but it boils down to APIs and programmatic control of the phone system.

The power of CPaaS is giving you the control of each call in a way that makes sense for your (or your business') needs. It lets you access information outside of the phone system (such as CRMs and other databases) to make decisions about how to route a particular call.

Another feature of CPaaS is the ability to get events out of the phone system - via webhooks or over a websocket typically. This gives you the ability to track a call's progress through the callflow, updating information in CRMs and other databases and lets you build robust applications on top of the phone network.

CPaaS providers often offer API access to manipulate running calls (such as programmatically hanging up a call, initiating a transfer, etc), fetching CDRs (call detail records - typically used when billing for calls), initiating new calls, and more.

A newer feature, a requirement of CPaaS providers these days, is having WebRTC-based phones (or a phone in your browser), minimizing the software needed to be installed and allowing companies to provide a branded phone in their web apps.

Most CPaaS providers allow you to process phone calls without being a telecom junkie by providing a simplified set of actions that may be performed on a given call. No longer do you need to know what the PSTN is or how SIP or SDP work - you get to build on top of an abstracted phone system and focus more on your business needs.

The competitive landscape

When you view the competitive landscape in telecom, it is easy to see that the big players (traditional telcos and UCaaS providers like Avaya, Broadsoft, and others) are recognizing the value of adding a CPaaS-type offering by purchasing CPaaS providers like Zang and Nexmo (via Cisco acquisition). Twilio stands apart as an independent CPaaS provider that IPO'd in 2016.

The market has shifted and CPaaS + UCaaS is the norm going forward; UCaaS companies are racing to catch up while CPaaS companies are trying to expand into more traditional telephony environments.

Technical Evaluation

Let's dive into a bit of the nitty-gritty and see how a handful of providers compare.

Real-time Call Control

Most CPaaS offer a small list of actions/verbs that can be returned from your program. The basics are covered by most providers.

Connecting callers to endpoints

When a caller calls in, typically you want them to talk to someone (or several someones). Below is a quick chart on the various endpoints supported by CPaaS providers for connecting the caller:

Action Kazoo Twilio Plivo Nexmo Tropo
Registered Device X X X X
SIP Endpoint
Conference X
Call Queue - X X X
User (find-me/follow-me) X X X X
Group X X X X
Page group X X X X

Some notes:

  • Kazoo is the only platform that allows devices to register directly to the platform to receive calls. Registration is the phone's way of saying "Send calls for me to this IP/port please". Devices can then move around (say a softphone on a laptop) but still be able to receive calls easily. The SIP endpoint, in contrast, is typically in a fixed location and is harder to move once setup. An existing PBX is the typical destination for SIP endpoints.
  • Twilio is the only provider that offers a "Queue" option in the public docs. Kazoo has a community-supported queuing applications called ACDc as well as a commercial offering called Qubicle, which can be leveraged for call queues. You can also simulate queues with conferences.
  • The 'User' endpoint is the ability to associate multiple devices with a user and ring all relevant devices when the user is dialed. Most providers allow you to specify multiple endpoints to dial but that association must be tracked on your side. With Kazoo, you can create a User and use that in your callflow instead.
  • The 'Group' endpoint is similar to the User in that you can add devices and users to a group and all associated devices will be rung.

    The biggest differentiate among the providers in this case comes down to the need for registration, insight into why a call failed to connect (some providers are quite opaque about the reason for failure), and additional features offered on each endpoint type (like setting custom ringtones).

Caller interactions

Most providers allow you to interact with the caller by playing audio files, generating dynamic text to read to the caller (TTS - text to speech), and collecting touch tones (DTMF) from the caller.

Action Kazoo Twilio Plivo Nexmo Tropo
Collect DTMF
Play Audio (MP3 or WAV)

Other basics offered

Action Kazoo Twilio Plivo Nexmo Tropo
Hangup a call X
Pause execution X
Record the caller
Redirect to different URL X
Reject a call X

Kazoo Differentiators

While CPaaS allows you to interact with phone calls at a higher level than processing SIP packets, the features above are fairly low-level as far as business concerns go. They make for great demos and getting a prototype out the door quickly.

Invariably, once you gain traction, feature requests come in and more functionality is needed. The question to ask is, do you have to do the work to implement the functionality or is it provided already?

For instance, say your prototype connects the caller, based on some fancy criteria, to an agent/sales person/fortune teller. You gain traction and now your callees (the agents/sales people/fortune tellers) would love to have a voicemail service in case they can't answer the phone (since most are using a personal mobile phone and don't want the caller to hear their personal voicemail).

Do you want to build a voicemail box?

With Kazoo, you can configure a voicemail box via API and add it to the callflow with minimal effort. With the other providers, you're looking at having to get the IVR right, get the prompts recorded, test all the paths through a voicemail box, figure out storage of the voicemail recordings, build an API for providing the voicemail messages, build voicemail->email and attach the recording, archive/delete old/deleted messages, and more. This is not quick to build and, frankly, most people don't consider voicemail a feature worth paying much, if anything, for; is it a good use of your time?

Kazoo offers a number of callflow actions, like voicemail, that allow you to add higher level, business-focused, actions to your call processing capabilities. A short list of highlights:

  • Call Parking
  • Directed / Group Call Pickup
  • Eavesdrop
  • Faxing
  • Hotdesking
  • IVRs
  • Manual presence updates
  • Time-of-day routing
  • Voicemail

Each of these features represents days to weeks of work to implement yourself (if you even can given the primitives offered by the other providers) and each has its own set of edge cases and intricacies that come with it. Instead, why not use the pre-built, heavily-tested callflow actions provided by Kazoo?

API control

The single largest difference between Kazoo's REST API and other providers is the sheer breadth of APIs exposed by Kazoo. Remember, Kazoo is both a CPaaS and UCaaS platform; on top of that, everything is API driven so you while you might start with the CPaaS-specific features, you can easily grow into UCaaS type services (like office PBX features).

Call Control APIs

Each provider allows you to list and control active calls. What controls you have vary; some allow you to redirect the executing callflow to your server for new callflow instructions; others expose the actions you can overlay on the call via the API and that's it.

Similarly, conferences and conference participants can be managed through most providers' APIs.

All in all, there isn't much that differentiates the basics among providers.

Kazoo API Differentiators

  • Multi-tenancy

    Kazoo is designed to be multi-tenant; you can have as deep or as broad of an account tree as you like. Most providers, like Twilio, Nexmo, and Tropo, don't provide multi-tenancy at all (Plivo does appear to though). As a service integrator, you will have to manage that hierarchy on your side. This means you have to build infrastructure to manage billing, resource usage, configuration, etc.

  • Carrier management

    Kazoo allows you to define your own upstream carriers, so even if you're using a hosted instance of Kazoo (versus running it yourself), you should be able to add your own carriers to you account and use them instead of the system's carriers. You can even setup hybrid situations where you route certain destinations to your carriers and use the system's as the default carrier group.

    None of the other CPaaS providers offer BYOC (Bring Your Own Carrier). This means that as you grow your voice traffic, you will not have levers to pull to manage costs. With BYOC, when it makes sense to, you can find your own deals on connectivity and seamlessly switch to your own carriers to save costs.

  • Finer-grained features

    Each API entity (such as devices or conferences) in Kazoo offers significantly more functionality compared to the other providers' equivalent entities. Of course there are some similarities but, for instance looking at a "device" in Kazoo, you can optionally define:

    • Call forwarding settings, including for failover (or just straight call-forwarding)
    • Call recording (both inbound and outbound) for the device
    • Call restrictions based on number classifiers (can call US DIDs, can't call international, etc)
    • Caller ID settings
    • Dialplan settings (allow users to dial shorter numbers and "fix" them - for instance the US used to allow 7-digit dialing and the area code was assumed based on the phone's location).
    • Do Not Disturb settings
    • Codecs available (both audio and video)
    • Custom music on hold
    • Custom presence ID (instead of the SIP username)

    There are other Kazoo-specific features on devices as well. Since users can own devices, you can set similar properties on the user and have them propagate to all devices (and define properties on the devices to override user settings).

  • Class-4 and Class-5 Switching

    CPaaS providers are typically concerned with a handful of phone system features - dialing endpoints, conferences, call recording, call queue, and phone number management most commonly.

    Kazoo, being a hybrid class-4 and class-5 switch, offers so much more:

    PBX functionality includes configuring users, devices, and callflows, blacklists, directories, faxes and faxboxes, IVRs, voicemail, and more.

    Configure connectivity features like carriers (resources in Kazoo parlance), ratedecks, PBX trunking.

    Configure reseller features like branding email notification templates and white-labeling Kazoo services.

Questions to ask a CPaaS provider

These are some good questions to ask your CPaaS provider(s) and to ask yourself how important the answers are to your needs:

  • Where are the voice servers located, geographically?
  • Where are the API servers located? Hint, some providers may have voice spread out around the world but API servers only in geographic location.
  • Where are the servers located (the data centers) relative to your users? To your carriers?
  • How is the networking built? Some hosted infrastructure providers, like AWS/GCE aren't well suited to VoIP traffic - are CPaaS providers piggybacking off that infrastructure or are they building out their own racks?
  • Is the CPaaS provider reselling another provider's service with better lipstick?
  • Can you extend the platform?


The market has spoken and they want UCaaS+CPaaS offered under one roof. The big UCaaS players have bought their CPaaS plays and are busy integrating them into the fold with varying success. Meanwhile Twilio remains an outlier and looks to be doubling down on being the CPaaS for the masses.

Kazoo offers you CPaaS + UCaaS from day one in a cohesive system. You can use as many or as few APIs and callflow actions as you need to accomplish your goals, while knowing that as you grow and need new functionality, Kazoo is there ready to provide it. On the off chance Kazoo isn't able to provide a feature, you can rest easy knowing the open-source nature of the project gives you the option to build it yourself and keep it private, build it and release it upstream for all to benefit, or support the project by contracting with 2600Hz to build the functionality for you.

Ready to kick the tires?