Looks like Apple just released beta 3 of the iPhone 3.1 OS and SDK to developers.

Also of note is that beta 2 will expire July 28th at midnight, so anyone on the beta better upgrade soon.

Once I install it tonight I'll report back with any changes I notice... like being able to make a phone call on the first attempt and not having it drop a minute later. Crazy improvements like that since beta 1 & 2.