Is there an Android SIP app running in the background?

Question

Android

How many applications have not tried, they do not receive calls if you exit the program (if it is running in the background). Only if you are right in the program and the phone is "on" calls are received. On different phones like this, on Zoiper, on CSipSimple.
It is necessary that, like regular calls, so that you can always accept if there is an Internet.

Answer 1

As far as I know, android has a built-in SIP client, I have one on HTC and it works in the background