Thread: S710 - Can't make a call

Hi, I hope someone can help/steer me in the correct direction.
Since last week, I suddenly can't make any calls from my phone. I can receive calls and I can both send and receive sms' but for some reason, I can't make a call. At the top of the screen, I suddenly have an E2. I remember the E from previously, but I can't remember ever seeing the 2 next to it.
I wwapped my sim to another phone which then works. I also put a friends sim into my phone, but it still doesn't work.

I have WM 6 Standard CE OS 5.2.1622 (build 18128.0.4.4) installed

Thanks for any help.

Followup: Well, I did not find what caused it to fail, but for some reason, it's suddenly working again. The E2 was back to E1 today (I know the E is EDGE, but does anyone maybe know what the 1 and 2 is for?).