For me, it was unlimited SMS. I refuse to spend 20 or so bucks a month on unlimited text, when I only pay 24 for unlimited data, it just doesn't make any sense from a bandwidth use stand point (SMS at most, should cost like 5 bucks a month).
To everyone wanting an invite, seriously just buy one on eBay. They're like 2-3 bucks and you can get the invite instantly. I paid 1.99 for one, and had the invite in my inbox a quickly as I clicked "pay now."