Last night, Apple released the second iPhone OS 3.1 beta to developers, roughly two weeks after the first beta was released, adding several new features to the growing list of iPhone 3.1 features, but also terminating the popular IPCC tethering hack.

While the first SDK beta introduced a handful of new, but only moderately noteworthy features, such as Voice Control over Bluetooth, the second beta gives developers running Xcode the ability to wirelessly connect to their iPhones for development and testing purposes.

This will give the developer wireless access to all the same features he would have if connected to the iPhone via USB, and will be especially useful for developers who need the iPhone's serial port for other external add-ons while testing.

Unfortunately, this upgrade also breaks the IPCC hack that allows AT&T customers to tether their iPhones, despite the carrier's lack of support for the feature. This hack will work in OS 3.0 and the first beta of 3.1, but beta 2 locks it out.

For this reason, many users are opting to avoid the upgrade until another workaround is devised, and take this opportunity to further denigrate AT&T in the forums. A Macrumors poster iPhoneNYC said, "Only one thing stands in the way of the iPhone being fantastic in every way -- and that is ATT. Why ATT needs to hold back on tethering when iPhone users in many other countries can use it is anyone's guess but it is clear that ATT is the weak link in the iPhone chain."

Aside from the broken hack, APIs that give the ability to overlay graphics over live video (a la Augmented Reality) have reportedly also been included in this version, and video editing has been made non-destructive, letting users safely roll back changes they may have made.

The list of known new features is still fairly brief, so Betanews will post updates as more features are uncovered in the SDK.