We are by no means as low as most of the other folks posted here, but we downgraded from AT&T to T-Mobile last year. Our AT&T plan, with a corporate discount, was $147/mo for three smartphones and 15GB of shared data. Our T-Mobile plan after we switched a year ago was $140 for 3 smartphones with unlimited talk, text, and data, including (reduced speed but largely adequate) international text and data in 140 countries, and Netflix. My husband just found out that they offer a Veteran discount (he is a Navy veteran) so for the time investment of a short phone call we have the same plan for $90 a month, and it's $10 a month for any additional lines we add when our younger kids are older. We ran the numbers on all the various lower cost carriers, but wifi at work is a PITA and my teenager uses so much data that Ting, Republic Wireless, etc, didn't come out in our favor.
I know $90/mo is not the low Mustachian target, but for 3 smartphones with unlimited talk, text, data, Netflix, and international text and data, it is a reasonable solution for our family. Granted it won't apply to everyone, but if anyone reading this is a veteran, it's a pretty nice deal. I know they also have a senior plan which is I think $60/mo for two lines. My in-laws pay an obscene amount of money to stay with Verizon, but eh, they can afford it and they are not very adaptable. We tried to get them to consider it, but it ended up not being worth the "trauma" of change for them.