GSM Modem & SMS to AB PLC Hardware

Hi, Interested in finding out from others what worked, what didn't and what to be weary of. I have an application where we need to receive data from a 3rd party via a primary source of SMS message and a backup via modem/dialup. I am lead to believe that we will need to read and write to the GSM modem with At commands. I have seen some sample code on the Rockwell site and it looks doable from an SMS messaging perspective.
Can someone enlighten me that the secondary modem/dialup scenario via the same GSM modem will also work. i.e we will be able to pole the GSM modem for AT commands and when an SMS AT command comes in we can read that data in and respond via AT SMS commands and when a dial-up/data AT command comes in we can react and read that in and respond via dial-up/data.

I get the impression that this is going take time to achieve - reading modem manuals, and formulating PLC code.

Thanks for your feedback.

Westermo has good examples.
Go to: http://www.westermo.com/web/web_en_idc_com.nsf/AllDocuments/6AA513A42FDD1A52C125788E00391312

Thanks. have had a look and there is some useful doc's.

keen to get an understanding that we can (via the PLC) listen out for incoming AT commands and when a precursor AT command for SMS comes in it will initiate, interpret and respond via SMS and when the alternate precursor AT command for dialup/data come in it will initiate, interpret and respond via dialup/data.

Hi, And a follow up. Since were moving things related to string files then is the limit of my message out 80 / 82 characters or can i feed more than one string file out to the modem in one message ie send one string file then follow that up with a second before sending the message. And the reverse for receiving messages can i read in 80 characters into a string and then the next 80 characters into a second string file. I note on one modem I've been looking at the spec's on that it has a character limit of 160 characters.