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.
Free users can get 60 voice minutes, 500 messages, and 3 groups of 50 contacts for their first line. That probably won't be enough to convince the average user to ditch their current phone number, but for a new business line (or a throwaway), it can be great. If you need more lines, messages, or minutes, prices range from $10-150/month, with unlimited texting coming in at the $25/month tier. Check out more info on the pricing structure here.
The app is live on the Play Store now.