Calling works fine for me (2+ hours yesterday). Connectivity is fine (LTE and 3 different wifi networks). Overall it's pretty functional. I have has random crashes here and there with some freezing. A few 3rd party apps have funky layouts, lost function and some don't work at all (eBay and find my phone crashes consistently for me). It's a first beta, if you can't deal with an imperfect phone don't touch it. If you're simply just curious it's probably not worth it. Not sure if you can downgrade (read some twitter tidbits about it being possible).
Forgot to mention I'm getting only maybe 50%, maybe 60% of the battery life as iOS 6.