Well considering the two north american iDEN carriers also run CDMA, a hybrid phone sounds good. A CDMA/IDEN/EVDO phone would be great, though it might be huge.

Also as part of Motorola's specification, an iDEN device has to have an external antenna since the frequencies are so low. (800MHz range) That's also why you frequently see Verizon phones with stubs or extendable antennas. Verizon is an 850MHz carrier.