You might need to create a new thread for your question. This thread is using for hardware compability. It's a wrong place to post question here.
Regarding to your question, there is no big difference in trixbox between installing GSM card and other cards. We have developed a newer chan_extra for GSM cards. You have to create your own custom trunk when configue on the trixbox web page. Please see [url=http: //www.chan-extra.org/index.php/Main_Page]here[/url] for more.