This talk concerns the design and optimization of Land Mobile Radio (LMR) systems, of which cell phone networks are the prime example. LMR systems are fairly complicated communication networks - - they typically involve hundreds or thousands of portable transceivers and fixed repeater stations. Often, the repeaters are located in such a way that they can interfere with one another if they operate on nearby frequencies. Additionally, since the radio spectrum is at a premium, there are many other systems with which any given system has to avoid conflict. These other systems provide a complicated and shifting network of constraints, especially as new radio systems are constructed or regulations change. On the other hand, there is a trend towards the creation of large, fault-tolerant systems for emergency communications. In this talk, I outline the problem of assigning frequencies to a network, discussing how the physical and regulatory constraints are implemented in a largely automated way. The primary example is that of a proposed emergency communication system in New York state and features some high-fidelity models of this network.