At the very least, we can give Sprint credit for actually acknowledging when the discount pricing will end. It's not unusual to see companies tout promotional subscription prices without actually admitting that they'll eventually go back up. And if you're just looking to save some cash for the next year, Sprint's offer is a pretty good deal. In comparison, you'd have to pay $180 a month for five unlimited lines on T-Mobile, or $270 a month for AT&T.
If you just need one unlimited line, you can save $10 on Sprint for the next year ($50 a month). It's also worth remembering that the company's unlimited offering comes with some compromises. In particular, streaming video is limited to a 480p resolution and streaming music is limited to 500kbps.