Some information is not completely accurate in the last post. iDEN, and GSM are TDMA.... Time-Division Multiple Access, where multiple conversations occur on the same frequency in different time slots, and because control channels are used, both are trunking formats.
FDMA is what regular trunking that we normally associate with police comms (EDACS, APCO16 [SmartNet, SmartZone, etc, and APCO25 phase 1) as a control channel is used to divide the frequencies used among users and only one conversation can fit on a frequency.
But that's not really the point. iDEN is an ancient Motorola proprietary standard (like the SmartNet control channel) nearing the end of its life. the voice-coder was originally VSELP (also motorola proprietary) but has more recently been using AMBE. The frequencies are coded using AM as well. Batlabs.com, while it hasn't been proven, states that if you cram an IMBE codeplug into a VSELP Astro radio (because the IMBE allows for "digital carrier squelch" operation, meaning any digital audio will be decoded) will allow for the decoding of iDEN frequencies- of course how it would handle the time-slotted audio makes it hard to believe.
Aside from that, NexTel here, and probably Telus MIKE up there is setup like any regular cellular type system with antennas mounted in a triangular pattern for 360* coverage. Each "side" of the cell station is in itself its own trunking system. So when traveling around it even in a circle during a call could cause the phone to hand-off three times as it goes around... This makes making a scanner that could follow all the handshakes impossible to build, especially since towers are so close together and such low power. Public safety systems are almost completely opposite with fewer towers using higher power and coverage large areas with omnidirectional patterns.