Anyone have 2 lines on their phone plan?

I typically just do a pay as you go card/phone, but my sis wants to get a plan for us both, so we have wifi anytime. It will be 15 more bucks a month than my pay as you go, just for that feature (I have enough text/minutes with the pay as you go, but not much wifi data). Anyone know a plan that is reasonably priced for 2 lines ?? I'm looking into Mint Mobile, and Boost too. Thanks!!