question

All calls are answered on my cell phone. Sometimes when calls are placed to my office my cell phone doesn't register a RingCentral call. 

The RingCentral Mobile provides a very robust set of features that nearly mirrors the full blown desktop application. The trade-off in developing a feature rich application, is that it can make setup and configuration a bit more complex.   The issue above is most likely a configuration issue.  If anyone else is experiencing this, please let us know.  There are multiple settings to check both in the web portal as well as the mobile app itself.

A few things to check are....

1. Double check the DND setting on the mobile app
2. Make sure have either a wifi, or data signal
3. Check the call forwarding settings in the web portal ( are you ringing the mobile app, or forwarding to the cell number?) 
4. Are calls going to voicemail?  If so see: Troubleshooting Calls Going Straight to Voicemail
   
   

Dropped calls, interruptions in service, spotty or static calls, calls with broken speech

These are all symptoms of a network issue. If the troubleshooting steps below do not solve your problem, then please open a support case so we can further troubleshoot the issue. 

1. If you have both a wifi and data signal available, try to toggle the settings on your phone to see which gives you the best quality for that given location.
2. If you do not have a wifi signal available, keep in mind that the quality of the voip call can only be as good as the phone's 3g/4g signal. If you are in remote location, or some place where you simply do not have a quality signal, then some options would be to forward calls to the cell number instead of receiving them through the mobile app. For making outbound calls when there is not a quality 3g or 4g signal, you'll want to use the RingOut feature: Enabling RingOut on your RingCentral Mobile App
   
   
3. If the signal appears strong, but you are still experiencing quality issues, then you'll want to do some network testing. If the quality issue are with your wifi signal, then refer to the following Community topic for to assure your netork is configured correctly. Network requirements, and troubleshooting call quality issues.  If the network configuration is correct, but problems persist then continue with the PingPlotter test in the article. 
4. You can also rung a PingPlotter test directly from the mobile device with PingPlotters app for iOS which you can find here.  If you open a case be sure to include a copy of the PingPlotter report in the case. 
   
   

Updated to iOS10.2 and now RingCentral calling through LTE no longer works. I also called up tech support and they think it's my phone provider. Called my phone network provider T Mobile and they have there engineers looking into it but I'm getting the impression that's this is a iOS issue

This is a relatively recent issue that occurred with T-Mobile users who upgraded to iOS 10.2.  This was a result of the carrier supplying  only an IPv6 addresses, instead of a dual IPv4/IPv6address which it usually provides. Our engineering team has been preparing for the use of IPv6 addresses for quite some time and we already have a fix in place which has already been pushed to most accounts and we expect to be done by Jan 13th.  If this issue is still impacting you you we can resolve this. See the following topic for more details and instructions:  Mobile App: T-Mobile users unable to make or receive VoIP calls after upgrading to iOS 10.2