Thank you very much for the reply.
On the PLC side I have:
9600, 8 data bits, 1 stop bit and no parity
1000ms on expiry of character delay time
RTS/CTS with wait time for CTS=ON of 1000ms
On the modem side I have:
Auto bounding AT+IPR=0
And AT\Q3 for the RTS/CTS
I have notice that when I send a string with the ' at+cmgs= "number" $r$l "text to sent" $1A ' It sends the sms without the @ characters, but if I wait for the > charater and then send the text, it fills the sms with the @.
Thank you for the help