I understand it is not the (best) way to go, but some customers really want it and may help them to switch to OCS. I do not understand why you say the buttons won't work. You only have numbers and * and # signs, but it should be posible to dial telephone numbers and answer using the OCS SDK, as you doo with Skype, for example.
Would like to hear opinions about people who have used devices similar to the one I referred in the original post, but I guess there are not many 
Anyway, thanks for the answer.
Regards,
Cristian