Cannot receive SIP-register response after enabled 3G mobile data

```
What steps will reproduce the problem?
1. Turn on Wifi, turn off 3G mobile data
2. Start imsdroid and make a successful sign-in
3. Turn on 3G mobile data (while wifi is still on !)
4. sign-out
5. sign-on again => imsdroid cannot receive 200 OK
6. after that, cannot make a successful sign-in, even killed the app, or turn
off 3G. Need to reboot the android phone in order to able to successfully
sign-in .

What is the expected output? What do you see instead?
in step 5, the sign-in icon changed to a triangle with "Cancel". If I press
Cancel, it returns back to Sign-in icon; or wait about 50 seconds, it will
timeout and retrun back to Sign-in icon

What version of the product are you using? On what operating system?
Phone = LG Optimus Black P970
OS = 2.2.2
Kernel = 2.6.32.9
firmware = LG-P970-v10b

Please provide any additional information below.

```

Original issue reported on code.google.com by `mingwaic...@gmail.com` on 27 Sep 2011 at 5:06