"T-Mobile's deal that lets four lines share 10GB for $100 a month" ... not quite true. It is 2.5 GB per line until start of 2016. That is PER line allotment, no sharing.
I just looked at my verizon page. Our 10GB per month @ $80 shared plan is no longer available. Now, the tiers are 6GB @ $70, 8GB @ $85, and 10GB @ $100.
Which is all strange because it was only a few months ago that they upgraded us from 6GB @ $80. I guess they were trying to keep us at the $80 plan instead of just discounting us to $70.