I've got a Sprint Airave, which is a femtocell. That's probably what you're thinking of. Sprint gave it to me free because the signal at home is crap (even though my old WinMo phone was fine). I had them expand the coverage so I'm still able to connect to it outside. It seems to have taken care of dropped calls and weak signal for my i5. My wife is still on her WinMo phone so is also able to take advantage. I haven't heard any complaints so I guess it's working for her.
I don't know what carrier you're with, but the Airave hooks into my internet connection. The package included a GPS module with a very long cable. You have to put the module near a window so the Airave can get a GPS signal. And your internet connection has to be a certain speed for it to work. Hooking it up was a PITA, but once I discovered that tossing out all the directions and then just plugging it into my internet switch was the way to go everything was fine. My i5 already rides my wifi at home so that's a separate issue. I've switched WiFi off and it's just impossible to do anything even with the Airave. I'm with Sprint and my area (Phoenix) doesn't have 4G yet, so getting this out of Sprint for free (the unit, activation, and monthly charge) was my way of equalizing things. They charge me an additional $10/month now just because I have an iPhone 5, but I'm not paying for the Airave or TEP (Total Equipment Protection) so I actually come out ahead.