je viens de trouver ceci
Suisse CHE Sunrise 900/1800
Swisscom 900/1800/ 3G 2100
Digicel 900/1800
donc
Write Command
Return
Reference
AT+SBAND?
+SBAND:
OK
AT+SBAND=
OK
value:0-10
value
0 GSM900
1 DCS1800
2 PCS1900
3 GSM850
4 GSM900&DCS1800
5 GSM850&GSM900
6 GSM850&DCS1800
7 GSM850&PCS1900
8 GSM900&PCS1900
9 GSM850&GSM900&DCS1800
10 GSM850&GSM900&PCS1900
cell.println("AT+SBAND=0 OU 4");