go4computers via eBay offers the Unlocked Apple iPhone 4S 16GB Worldphone for GSM Networks in Black (pictured), model no. MD234LL/A, or White, model no. MD237LL/A, for $619 with free shipping. That's tied with a deal from last week and the lowest total price we could find by $30. (However, it was $19 less in March.) It's powered by the Apple A5 dual-core processor and features an 8-megapixel camera which is capable of recording 1080p video at 30 fps with image stabilization, dual-antenna system for faster downloads and improved call quality on GSM networks, AirPlay Mirroring, Siri voice-activated assistant, 8-hour battery life, and more. It's compatible with GSM networks such as AT&T, T-Mobile, Vodafone, and more; it can't be used with CDMA networks such as Verizon or Sprint.

Note that on some networks, such as T-Mobile, the phone will not operate at 3G speeds.