You can check the band in use with this command: gsmctl -A AT+QNWINFO
The response should look something like this:
+QNWINFO: <Act>,<oper>,<band>,<channel>
Where:
<Act> - access technology type (e.g., WCDMA, GPRS, etc.)
<oper> - network operator in numeric form
<band> - the frequency band
<channel> - channel ID