SLC5/03 to 1500 comms with phone line

Hi there...
...Would appreciate if some1 could help me out a bit here.
Basic:
Main PLC SLC5/03 x 1
Remote PLC 1500 (LRP C) x 4
All these connected to Westermo TD-33, a phone line.
Philosophy:
Remote PLCs sends signals (alarm bits and Flow rate) to Main PLC and (then Main PLC sends all the signals to the SCADA).

Remote 1

signals ModemON
---|N7:0|-----------()
modemON Write to Main
---||-----------(MSG)
MSG sent HangUp
---||---------------()

But a little bit more guidance I'd need, obviously
Just bare in mind, that PLCs are on site already.
Configuring modems (AT) is not an issue, just that ladder.

Cheers
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