Mobile phone and communication system switching method

A mobile phone, comprising:

• a first communication system;
• a second communication system;
• a processor;
• and
• a storage system storing a current table which stores a first relationship between current and signal transmission power in relation to the first communication system and a second relationship between current and signal transmission power in relation to the second communication system, and one or more software programs in the form of computerized codes operable to be executed by the processor, the one or more software programs comprising:
• a service determining module for determining if the mobile phone requires a voice call service according to user input;
• a strength obtaining module for obtaining a first received signal strength indication in relation to the first communication system and a second received signal strength indication in relation to the second communication system if the mobile phone requires the voice call service;
• a power calculating module for calculating a first signal transmission power in relation to the first communication system according to the first received signal strength indication and a second signal transmission power in relation to the second communication system according to the second received signal strength indication;
• a table searching module for searching the current table to obtain a first current according to the first signal transmission power and the first relationship and a second current according to the second signal transmission power and the second relationship;
• and
• a system selecting module for selecting one of the first communication system and the second communication system to provide the voice call service based on a smaller one of the first current and the second current.