connectivity for an existing system makes sense at a retailer with a physically persistent location.. but if you are looking at being mobile, you need data connectivity.

I think this breaks down easily: 1) You DO have existing device and data plan, and need to be mobile: Square (or similar service) makes sense. 2) You DONT have existing device or data plan, and need to be mobile: GoPago

I think the evolution of phones tends towards people already carrying a smartphone with data plans, making square (or other service only -- no hardware solutions) somewhat more attractive with its rates.