I think about it because AT&T is terrible in my building. I can't make calls 50% of the time in my own apartment. Wired lists 6 Reasons to Jailbreaked the iPhone...

 

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1. Google Voice

Apple recently rejected and banned Google Voice apps from its App Store. The apps would have augmented the search giant’s new voice service, which enables users to rely on a single phone number to ring all their phones, while also delivering the gift of free text messages, voicemail service and cheap international calls. The move stirred so much controversy that even the Federal Communications Commission is inquiring about the prohibition.

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2. Unrestricted 3G Privileges

AT&T iPhone owners pay $30 per month for “unlimited” 3G data access. But your access isn’t truly unlimited, thanks to restrictions that Apple imposed on some apps. SlingPlayer, an app that streams television from a Slingbox device, was crippled to work only on a Wi-Fi connection at the request of Apple and AT&T. And the Skype VOIP app only works on Wi-Fi, too, rendering it impractical.

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http://www.wired.com/gadgetlab/2009/08/reasons-to-jailbreak