FreedomPop has just gone into open beta!
It is a new MVNO (mobile virtual network operator), which means they use the same 4G network as Clear
Check Clear's coverage map first to make sure you're in a coverage area:
CLEAR | 4G Wimax Internet Coverage Map with Service Area.
What's the catch? There isn't one really.
You'll need one of their two devices, which are also technically free - you have to put a deposit which you get back if/when you terminate service
USB 4g dongle (for internet on your laptop) - $50
Pocket Wifi Device (for wifi hotspot for up to 5 devices) - $100
iPhone 4g case (currently sold out?)
If you have a WiFi only device like an Android tablet, you could install Google Voice and use this as a free VOIP phone line! 500MB/month is more than enough for basic emailing/texting
You can even earn more monthly bandwidth by inviting friends.
I just signed up myself with the Pocket Wifi device and I can't wait to try it. Let me know if you have any questions and I'll answer them to the best of my ability.
Enjoy!