The biggest deal with femtocells here in the States (Colonies) is that cells tend to latch on to the _strongest_ signal. Some phones have preferential selection for type of network, but very near the femtocells I have seen demonstrated here (within 20-25ft / 7-8m), the femtocell effectively BLOCKS OFF connection to any other signal nearby for cell reception.
That means if you use one in an apartment complex, you will probably have the neighbors' cells on your femtocell, similar to the way they slurp off your wifi now.
This makes is amazingly easy for fraud, etc. because tweaking your own "cell tower" does not reveal the phone number, but does show the ESN or other phone identifier and network ID, which can then be used for man-in-the-middle attacks for using other's network charges or close off cell access completely for those "late night visitors" that don't want to wait for you to leave before stopping by.
All in all, just means that the average Joe will have the same capability as the Feds have had for decades now. All in the greater good, eh?