Because Cel-Fi systems generate boosted copies of the original macro network channels, there are no handoff issues between Cel-Fi systems or between Cel-Fi and the macro network. For example your phone might use signals from Cel-Fi and the network at the same time, and it would not know the difference. So unless there is an area that is not covered, you should expect a seamless call experience when entering or existing the Cel-Fi coverage area.
This is in contrast to a consumer femtocell (sometimes referred to as a microcell). Handsets must be uniquely registered on these devices and capacity is very limited. They also do not allow calls to hand-in from the outside network (i.e. if you make a call outside, or indoors where the macro network is handling the call, the call will drop when you move to the femtocell coverage area).