Hang up with wifi. There are no K coins. You must use GPRS. You don't need to turn on the GPS when you hang up, but you need to keep the program running in the foreground. Can't go back to the desktop to do other things or lock the screen.

In addition, China Telecom's 3G network hangs up without K coins. I don't know if Unicom Mobile's 3G network will work. I use mobile GPRS, no problem.

These are all my own experiences, and I hope I can help you.