If there is a solution for UMTS (W-CDMA) coming, we don't need the expensive nanoBTS anymore.
BTW I've still one for sale ... see at http://umts.zerber.us
There are cheap W-CDMA BTS's out there, like Netgear DVG834GH, AT&T 3G Microcell, Alcatel-Lucent 9365 or the Vodafone Access Gateway you can buy in England for just 160 GBP each.
All the femtocell's I know have built in GPS for timebase and security reason, so there is a lot to do for our purpose ...
I guess the future is W-CDMA and I hope there will be openUMTS available soon ;-)
Regards from Switzerland