thanks for your answers.
acejavelin: No one can make any external call.
ralph: I just called them, they say the trunks are OK but they are receiving an Alarm. Actually it shows a MAJOR alarm.
I remember just adding a String to dial after 9 for international calls, from here (Mexico) it would be 00 + country code + area + number.
somebody had to make a phone call to China and couldn't make the call. now I can't make any call being local, Int; or to cellphones.
Our provider is bad, he will check the problem later today, unsure about the time.
Hopefully is just a configuration issue and not a hardware issue.