Tmobile has a sort-of unlimited option.  You decide how much 'high speed
capable' internet you want per month 500M, 1G, 2G, IIRC).  When you
exceed that, you 'automatically' fall back to slow (I'm guessing 56K).

 

Beware that even if you force your phone (or whatever) to slow speed
TMobile still counts the usage as 'high speed capable'....

 

Rusty