Q: Is there in warp gsm module driver an option that we can fix the card to the provider? We have a problem, that the gsm card goes in roaming... how can we prevent the foreign operator registration?

A: First you need to determine the mobile country code (MCC) and mobile network code (MNC) of your desired provider. Executing the GSM command at the Asterisk CLI will provide a list of providers and this code. The specific query command format would be 'gsm send at AT+COPN'. Otherwise you can also try referencing this webpage - http://en.wikipedia.org/wiki/Mobile_country_code

Once you have this you can set the current GSM/UMTS network operator using the following command. where 'yyyzzz' is the number described above. To set this each time on boot up you can insert it into the /etc/asterisk/gsm-init-file.
Specifically the format of the line would be the following:

at+cops=1,2,"yyyzzz" OK 1 2