They carry primarily voice but as IP data packets. These IP packets might be sent over the cisco VPN to provider (Voda/Orange/etc), although I'm guessing here. I'm sure they will carry data too, but why use data at home on your own broadband connection, when you can use wifi! (unless your phone doesn't have wifi). So I| think their main purpose is for the voice aspect.
They are like mini cell transmitters for your own home or office which you plug intop your broadband connection, so you get better phone signal in a dead spot (stop you hanging out of windows to get a good signal!).
They normally have a 4 calls at once limit, but can have up to 32 phones registered with the unit. Phones have to be registered though, so you don't provide service to every passing neighbour, just phones you choose to allow.
I haven't read it myself, but I guess this link might help...
http://en.wikipedia.org/wiki/FemtocellHope this helps
Mike