Mixing VOIP & Cellular calls with carrier WiFi calling causes inability to place Cellular calls

Number:rdar://29938170 Date Originated:1/9/17
Status:Open Resolved:
Product:iOS + SDK Product Version:10.2
Classification: Reproducible:Always

When T-Mobile's WiFi calling is in use, after receiving simultaneous calls to phone app and our VOIP app and ending one of the calls, attempting to place a call with the system dialer results in call failed.

Steps to Reproduce:
Make sure your carrier's WiFi calling (T-Mobile or Verizon) is being used.

1. Make a dial through call 
2. Receive in inbound call to VOIP app (hold and answer)
3. Switch between calls to verify audio on both
4. End the line 1 call. 
5. Try to make a outbound call using Line 1.

Expected Results:
You should be able to place a call from the system dialer.

Actual Results:
Attempting to place a call from the system dialer results in Call Failed.

iOS 10.2 (14C92)

This only happens when the carrier's WiFi calling is active.

iPhone 6, 128GB, T-Mobile with WiFi calling, iOS 10.2 (14C92)

'sysdiagnose_2017.01.09_15-58-20-0800.tar.gz' was successfully uploaded.


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