I have a TMobile LTE SIM in my Surface which also gives me unlimited text messaging. I would love to be able to send outbound texts, but can't figure out how to do so. Inbound texts go to the messaging app, but I can't figure out how to enable the outbound messages. I think I need to input the outbound SMS center, but don't see anyway to do so. Does anyone know whether this app or a different one supports messaging through cellular text messaging service (e.g. not Google Voice or something).