Hmm, if i am not wrong, the ";" will cause the modem to return to standby and ready to accept further commands once the current command is executed as mentioned by Muhammad Fauzan. If you do not include the ";" however, the modem will stop accepting command and wait to negotiate with the remote modem instead, which is not the case here since i am doing a connection to a telephone in voice mode.

The escape sequence "+++" in my opinion only works in data-mode, that is, after the local modem established a connection with remote modem and is currently in data transferring progress. The "+++" mentioned by you will "force" modem out of its data transferring process, and prepare to accept command instead.

Correct me if i am wrong. Thank you very much for your feedback!