Symptom:
We have the feature called "Call preservation" at the moment on Cisco Jabber Android. 

The explanation of the concept can be found at http://www.cisco.com/c/en/us/products/collateral/unified-communications/jabber-voice-android/datasheet-c78-730692.html

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Call preservation keeps your call connected when you receive a mobile (Global System for Mobile Communications [GSM] or Code Division Multiple Access [CDMA]) call while on an Internet call. You can retrieve the Internet call by returning to the Cisco Voice Jabber for Android application and resume the call.

The above explanation seems to confuse customers as the Word Call preservation could mean that the call would be preserved on the event of connectivity issues to the CUCM, like we have for the wired Cisco IP Phones but whereas in Jabber Android, all that is done is the VoIP call is being held when we get a call on the GSM, this should be given another name like "Call Held" or something else

Conditions:
When Jabber Android moves from WiFi to GSM Data connection, the active call wont be preserved, this is by design