Default SMSC number problem

I just bought motorola a3100, and I have a problem regarding sending sms.

Everything works fine, I can call everybody, but I cant send SMS messages. If I get to inbox - tools - options, and under "tap an account to change settings" messages has (*) symbol, and I can't change options in messages (service center number)
so please, is it possible to change default value of service number from registry, or any other way?

thank you very much