Andrew,
Unless the provider your using is a real cowboy outfit, then they're most likely to offer an XML, XML-RPC or a TCP method.
In which case you probably looking at now more than an hours work making the code match the interface..
So pretty much all you want is there.
Or, even simpler, just use a GSM modem.. There's a good seimens unit for about £40. And the SMSBroker already has the interface for that.
