I don't know about the cellphone thing, supposedly Horizon has tested most scenarios and nothing so far has caused problems. I got a DVD from Horizon that goes into great detail about how Spread Spectrum works. The basics are these:

It operates on 2.4 GHz (gigahertz) rather than 72 MHz. 2.4 is the same band that medical equipment in hospitals as well as some cordless phones transmits on. FCC restricts the output for DSS transmitters to 1 watt, and the biggest hurdle toward getting it to work for r/c planes was the signal strength at any kind of range. The dual receiver system ussed helped solve this. DSS is immune to RF interference from gasoline engine ignition systems, as well as metal-to-metal vibration RF. When you mount the Rx in the plane (actually two Rx's connected with a 6 inch pigtail), one has its antennas 90 degrees to the other's, so they get a slightly different "picture" of the signal. The antennas, BTW, are only about 2 inches long, so you no longer have to worry about routing a long antenna wire.

When you turn on the Tx, it scans the entire 2.4 band and selects two unused "channels" and locks onto them before it will transmit. This is why you don't have to use the pinboard, or frequency control with 2.4 GHz. Each radio that gets turned on will not transmit until it has found an unused channel and locks onto it. The receiver has to be "bound" to the transmitter in a procedure you perform when setting up the radio; when this is done, the Rx will ONLY respond to signals sent from the Tx it is bound to. If you have several planes in your radio (the DX-7 has a 20 model memory), each Rx has to be bound to the Tx only once. When you select the plane from your Tx menu, only that plane's Rx will respond, so it is impossible to fly the wrong plane.

I got my registration info for Joe Nall in the mail the other day, and they give quite a bit of attention to using DSS at Tripletree this year. They say that up to 40 planes can fly in a single area on DSS before the band is full. They will still require Tx impound, but DSS doesn't have to use the pinboard system. With only 7 flight stations in use, ther will be NO problems with too many planes in the system.

I'd recommend going to Horizon's website and requesting the DVD about Spektrum.