Официальный ответ производителя:
Цитата
to answer a call you have to wait for the RING indication that is sent just after the #ECAM: 0,6,1 URC.
at+clcc
+CLCC: 1,1,4,0,0,"+39xxxxxxxxxx",145,""
OK
ATA
NO CARRIER (not ready)
#ECAM: 0,6,1,,,
RING
ATA
#ECAM: 0,3,1,,,
OK
Only after #ECAM or RING the module is ready to answer a call.