I have setup FollowMe on my internal extension with the following settings:
Initial Ring Time: 0
Ring Strategy: ringallv2-prim
Ring Time: 30 seconds
(to allow sufficient time for my cell phone to ring - for testing purposes I have disabled Voice Mail on my cell phone)
Follow-Me List: and #
(have listed my own extension in the list so that I can see the incoming calls while I am already engaged on the phone on the first line - I have enabled Call Waiting on my extension)
Destination if no answer: Voicemail: <myextension: unavailable>
I should add, I have setup an incoming DID route and set its destination to my extension, which simply goes directly to FollowMe.
Here is the outline of the problem:
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When I test this setup from an internal extension phone (i.e. use another internal phone to call my own extension), this works perfectly fine and for each ring strategy - the setup works as expected and my cell phone rings until the 30 seconds ring time is reached and then the call is put to voice mail.
-
When I test this setup by calling my DID from any external phone (i.e. from my analogue line from home, from another mobile phone, Skype, etc.) the setup does not work as expected. When the call comes in, I can see my extension ringing and immediately (after few seconds) my cell phone starts to ring, however after few ring tones the call to my cell phone is unexpectedly terminated and on the remote external phone I get the message from the telecom provider, that the call can not be established and after that, my call is terminated. This issue occurs almost exactly the same for any ring strategy I choose - the only difference is that some times the cell phones rings 1 or 2 seconds longer. Obviously, I expect the cell phone to ring until the 30 seconds limit is reached and then the caller should be put to voicemail - this unfortunately does not happen.
At the end, I should add that our internal PBX uses a SIP trunk to an external PBX (both PBXs are the same Asterisk/FreePBX based), which then registers to an external VoIP provider. Therefore all incoming and outgoing calls go through the same route through the same VoIP provider. I have checked my cell phone GSM provider and the VoIP provider and neither cause the problem. Our network resources and network configuration also is not the problem.
Going to into Asterisk CLI shows, that the call is being made to my cell phone with making progress (etc), however then suddenly for no reason the hangup message throws in without any errors and the entire call is immediately terminated making the caller unable to either reach me or leave a voice mail.
I have looked everywhere and tried everything (even upgraded to the newest FreePBX version) - obviously to my best knowledge, although I must say although I am learning quickly, the Asterisk/FreePBX area largely remains to be explored by me 
Any help would be greatly appreciated.
FreePBX Core: 2.5.1.6
FollowMe: 2.5.1.8
Asterisk 1.4.17~dfsg-2ubuntu1
Thanks,
Ed