You can check the possible options, if you have a working setup, by the following command :
AT+COPS=?
It will give you the available carriers and the available options usable with them.
Answer format is:
+COPS: [list of supported (<stat>,long alphanumeric
<oper>,short alphanumeric <oper>,numeric <oper>
[,<AcT>])s][,,(list of supported <mode>s),(list of supported <format>s)]
An example answer:
AT+COPS=? +COPS: (1,"E-Plus",,"26203"),(1,"Telekom.de",,"26201"), (1,"Vodafone.de",,"26202"),(1,"o2 - de",,"26207"),,(0-4),(0,2)
tells that supported modes are 0-4, values from this table:
0 GSM
1 GSM Compact
2 UTRAN
3 GSM w/EGPRS
4 UTRAN w/HSDPA
5 UTRAN w/HSUPA
6 UTRAN w/HSDPA and HSUPA
7 E-UTRAN
Sources:
https://stackoverflow.com/questions/33345651/atcommand-atcops-gives-undefined-return
http://m2msupport.net/m2msupport/atcops-plmn-selection/