Google Voice is a great service for replacing your carrier's voicemail and texting options. If you need something that's a bit more robust, however, SendHub has launched on Android and allows business-class users to set up a phone number (or set of numbers) and get texting and calling for free or cheap, depending on what class of service you need.

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Free users can get 60 voice minutes, 500 messages, and 3 groups of 50 contacts for their first line.