switches - Ways of Switching between Two Sim Cards

I'm interested in building a circuit to switch between 2 sim cards, and found a design guide by GSM module manufacturer Telit. (New design guide link here, see pg. 16+)

In particular, "Figure 6" of this guide shows the use of a p-channel MOSFET to switch the SIM Vcc on and off, and there's a separate multiplexer for the data, clock, and reset lines.

I was wondering what the alternative ways of doing this were, and what affect they might have.

For example, would it be possible to remove the multiplexer and simply control the SIMs using the MOSFET, or would it be possible to use a switch on only the data line, and share the power, clock and reset between the SIM cards?

I know the voltage on SIM cards can be either 1.8V or 3V, so maybe sharing the Vcc line would cause issues?