If you have an old Android phone laying around and want to gain a second phone line or have the incredible urge to make calls from your tablet (requires a Bluetooth headset), then GrooVe IP is no doubt the go-to app. For a limited time, you can save yourself a few bucks and score this app for $2.10 (normally $4.99) in the Android Market.
So, what is GrooVe IP? If you haven't already guessed, it's a VoIP (voice-over-IP) client, which allows you to make and receive calls using only Wi-Fi. One of the best features of Groove IP is that it works hand-in-hand with Google Voice, so you get an all around, 100% free (aside from the cost of the app) solution for a second phone line. Setup appears to be a snap, too.
This deal ends at 11:00PM PST tonight, so make sure to grab it soon!