MagicJack, the company that makes the cheap internet phone, is coming out with one for the cell phone. It connects to your computer and when the cell is within 8 feet, you can connect. It's supposed to cost about $40 and it won't use any cell minutes when you call.
Here's some information from MagicJack's next act: disappearing cell phone fees by AP: Yahoo! Tech
The size of a deck of cards, it plugs into a PC, which needs a broadband Internet connection. The device then detects when a compatible cell phone comes within 8 feet, and places a call to it. The user enters a short code on the phone. The phone is then linked to the magicJack, and as long as it's within range (YMax said it will cover a 3,000-square-foot home) magicJack routes the call itself, over the Internet, rather than going through the carrier's cellular tower. No minutes are subtracted from the user's account with the carrier. Any extra fees for international calls are subtracted from the user's account with magicJack, not the carrier.
According to YMax CEO Dan Borislow, the device will connect to any phone that uses the GSM standard, which in the U.S. includes phones from AT&T Inc. and T-Mobile USA. At a demonstration at CES, a visitor's phone with a T-Mobile account successfully placed and received calls through the magicJack. Most phones from Verizon Wireless and Sprint Nextel Corp. won't connect to the device.
I have a Network Extender and while it seems the same, the NE has a GPS antenna for 911. It looks like if you called 911 with the MagicJack, your location would be where the internet hub would be. But the call would be free.