I was wondering about this -- why can't phone transceivers just switch frequency? I built an FM receiver from a kit once, and you changed frequency by screwing an iron core into a wound wire coil. If you screwed it past the radio stations you could get the telly audio.
A radio can only do so much.. Even with the ability to do some tuning, the physical antennas within a given device are going to be optimally tuned for specific frequencies. Outside of those optimal frequencies, the antennas are not going to be as efficient at their jobs, requiring more power and lowering battery life, as well as increasing the size of the phone (ever wondered why a free to air antenna has multiple elements? Why some antennas needed to be upgraded to support DVB-T rollout in Australia on different frequencies?). Right now, the modern smartphone has antennas for: * Cell net * WiFi net * Bluetooth (I get the impression some vendors fudge things and share this with WiFi) * GPS * NFC They use different frequencies and work at different transmission power levels and generally need separate antenna elements. Hell.. probably forgot some stuff.. In short, the radio is not the only part of an RF device that involves tuning.