Most pre-paid plans do not allow tethering (although it happens anyway). One that does is Ting
. However Ting is not an "unlimited" service. Instead you pay for what you use so you'll want to be aware of your average monthly useage when deciding if Ting is for you (and I'm not going to lie if your using more than 2GB a month, your probably going to be better off somewhere else, but they probably don't allow tethering and it should be cheaper than a contract). On the plus side Ting runs over Sprint and has access to Sprint's LTE network (most prepaid services do not have access to LTE) if it is available in your area.
Anyway if you (or anyone) do decide to go with Ting use this link https://zll4ogo6p.ting.com/
, you will get $25 of your first device or first months service and I'll get a referral credit :-)