This command is only available during a CSD call or a GPRS connection. The
+++ character sequence causes the TA to cancel the data flow over the AT interface
and switch to command mode. This allows you to enter AT commands while
maintaining the data connection to the remote device or, accordingly, the GPRS
connection.
OK
To prevent the +++ escape sequence from being misinterpreted as data, it must
be preceded and followed by a pause of at least 1000 ms. The +++ characters
must be entered in quick succession, all within 1000 ms.