If you regularly run into overages or speed limits with your monthly data use, Onavo Extend can help out. The free app reroutes your mobile Internet traffic through its servers and compresses data when possible so you don’t use as much of it. (Here’s a tip, though: if you don’t want the app to pester you when it’s turned off, go into its settings and turn “Savings Alert” off.)
Link: Onavo Extend (Free)