For cellular application, you need separate LNA+Mixer for 900Mhz and 2Ghz. After downconvection, the BB AMP, filter and so on could be shared by 900Mhz and 2GHz. Need an extra band selector.
A broadband (continuous) transciever will be almost impossible to do. Multiple band selected transceiver linked by switches is feasible.
The IF section can be shared.