It is often the case that if you have a jailbroken iPhone via ultrasn0w and use it with another company soon iPhone apropos convertura runs out with the message "no service" or "sim error". The simplest solution to this problem is to restart a few times until you get the iPhone back cover.
The problem with this solution is that we will move steadily becoming a nuisance and may even have the iPhone no signal several hours until you realize the problem.
For now the solution is working for me is:
1.-Go to Settings / Operator
2. Choose your company and remove the Automatic.
Also you can replace your iPhone Lockdown for this:
1.-Access files from your iPhone / private / var / root / Library /
2. Rename the original Lockdown
3. Download this lockdown
4. Metellus in the path before / private / var / root / Library /
5.-Restart your iPhone.
Usually, I've already several days without losing the signal without any problems.