You can set <AT+CRC=1>. Then:
URC <+CRING: REL ASYNC> will indicate a CSD call,
URC <+CRING: VOICE> will indicate a VOICE call.
By default it’s <AT+CRC=0>, Then only URC will be appeared for both CSD and VOICE call.
Another solution is to use <AT+CLCC> after receiving the , the response can also indicate CSD or VOICE call.