An App from June Fabrics that requires a one time fee (about $20) and no monthly separate rental and equipment fees from your provider. The only drawbacks are you need a cellular connection and a big enough data plan. It can work either tethered or as a mobile hot spot. We use it for our laptop and two Kindles. I do not use it outside of the US, but it is good for most of the US. With a 4G is is real good, 3G not bad and for slower connection, still works but often very slow. Other than a happy user I have no connection to the company.

Android
http://pdanet.co/

iphone
http://www.junefabrics.com/iphone/