Rich Communication Services Universal Profile (or Chat as Google likes to call it) is all about interoperability. The end goal would be for ALL carriers world wide, to standardize on RCS as their carrier provided messaging platform (instead of SMS / MMS). There are a lot of moving parts that will have to come together for this to happen, but some of those parts are starting to come together.

How RCS Interconnects

RCS is a combination of an RCS client on your phone and your carrier’s RCS engine. Carriers have 3 basic ways they can set RCS up:

1. Proprietary RCS (not Universal Profile) – This is the way some carriers currently have RCS implemented. For instance, as of the time of this writing, AT&T and Verizon both use proprietary RCS implementations for their “Advanced Messaging”. Unfortunately, this is a walled garden approach – by this I mean, an AT&T customer can currently ONLY send RCS messages to other AT&T customers.
2. Carrier Hosted Universal Profile – This is where a carrier chooses to roll their own RCS implementation, but does so in a manner that is compatible with the GSMA Universal Profile.  This requires a LOT of carrier knowledge / configuration as the carrier will have to work with other carrier hosted versions as well as cloud providers to make sure their implementation works as expected.
3. Cloud Hosted Universal Profile – This option is where a carrier signs up to use a third party cloud service. Several RCS cloud services are already in place (Google, Samsung and others offer RCS clouds). The advantage here is the carrier only has to interface with the cloud provider.
   

So, who can I send an RCS message to?

The short answer to this question is you can send a RCS message to any other customer that has an RCS client that is on a carrier your carrier can interoperate with (OK, not so short). Longer answer is that in North America today, Sprint, Rodgers, US Cellular, Google Fi, and some Verizon customers can send messages back and forth because they have apparently chosen the Google Jibe cloud option –pretty much every other carrier is still limited to only sending messages to other customers on the same carrier. T-Mobile has also started implementing RCS UP (currently only on two Samsung phones and they aren’t connected to any other carrier yet).

There have been conflicting reports  (thanks to Reddit users for bringing this to my attention) as to how T-Mobile is implementing their RCS stack. I’ve seen reports that they (at least initially) intended to use the Samsung Cloud and others that say they rolled their own either with or without 3rd party help. However, it’s my understanding that their implementation is using an older version of RCS UP that is causing some integration delays other carriers.

There is a Google Doc that is being crowd sourced that shows which carriers have had successful connection tests with other carriers here.

The Future

I know all of this sounds horrible and underwhelming, but it’s really not that bad. The GSMA has announced that all four major US carriers have agreed to implement RCS UP as well as 55 carriers world wide and they have teased other RCS implementations by the end of 2018. Once Samsung and Google get their interconnections worked out, T-Mobile customers with newer Samsung phones will be able to interact with Sprint and Rogers customers.

It’s really just a matter of time before RCS will be the default carrier messaging platform for North America and hopefully the world!

Current Status

There is an excellent Google Doc’s document that is being developed to track current RCS implementations.  You can view it here.