Could I buy an iPhone 5 or 5s on a Family Mobile plan?

I was just wondering if I could buy an iPhone from T-Mobile since I'm on the Walmart Family Mobile plan. I know that T-Mobile. And Family Mobile are connected, but I was wondering if this would cause any complications.

No complications at all. It may increase the cost if a data plan is not in the current plan

You'll still need the phone to be unlocked before you can use the phone on Family Mobile. Other than that, no issues at all. If you need unlocked iPhone 5S cheaper than retail, mail me.