We got our AT&T bill down from $120/mo (for two phones) to between $45 and $62/mo (for three phones). When it was just me (I was the guinea pig testing before we ported my wife's phone over), my bill would regularly be $25-30. Ting isn't "unlimited", but rather has a fairly simple "use your phone and we'll bill you fairly" mindset. They also have a calculator where you can have them login to your existing carrier, pull the billing details, and estimate your Ting bill. I was initially uncomfortable with the pay-per-use nature, but the reality has been that it's way cheaper for us. If you are a road warrior salesperson who never uses wifi, it may not be as good for you.
Naturally, since it's pay-what-you-use, tethering is perfectly fine.
Ting does offer a referral bonus where I think you get $25 and I get $25. I'm not shilling for them nor stumping for referrals, but if you do care to use the referral link, it's https://z9prmb2f3t5.ting.com/