I'm new to video conferencing units, so please be gentle :)
We have an HDX 7000 and some of my remote users (execs and sales) want to be able to use RealPresence Mobile on Android and iOS. I've tested the app (on android) while on our wireless and using the internal address all works well. I've also tested RealPresence Desktop on our wireless and again it worked fine. Anytime I use the external address (on the wifi or on LTE), the device rings and I pickup and it identifies the remote device's name, but the remote device (in this case the phone) just keeps ringing.
Thanks in advance
This is likely caused by firewall and/or NAT'ing of the endpoint IP address.
Do you have an Edge device such as an SBC, RPAD or VBP to assist with firewall/NAT traversal?
It may be that your issue is similar to the one on this thread: http://community.polycom.com/t5/RealPresence-Mobile/AT-amp-T-10-X-IP-Addresses/m-p/41383. (I think you noticed this yourself and posted there, too).
I've recently posted a response on that thread which might also be useful to you.