I don't think this would be a function of the DID number. I think a web script would recognize the sending telephone number of the SMS message and would then launch the same kind of call function that web call uses. Alternatively, a more complex SMS message could be used that uses the login info for the account. Either way, the calling would be launched by a script similar to the existing web call function.
What this would require would be an SMS gateway supported by i-p-tel.