Νομιζω οτι και αυτο που βρηκα ειναι χρησιμο:
Now a post to turn off EDGE network.
First you go in settings/network settings/Network mode, and you select GSM 900/1800. Now You've switch off 3G network
And now go in:
*#6984125*#
After 3 = Network
4 = Service Domain
And you select CS .
That's it
The Edge logo has disappeared, and when you want use it ( to send MMS, to go Internet) It is activated automatically. :)