Not using it, but appears they have an agreement with Sprint to use Sprint's network for coverage where they do not have a network. Their network is small, so depending on where you live you could be using Sprint a lot. I have Sprint, I'm fine with it.
Your info does not show where you live, I would be real careful to understand the impact of continual roaming or "partner services" on your pricing plan if you do not live in an area covered by their network, or if you travel off their network often.
