As the "Mars Packing List" on NASA's SpacePlace website points out, there are no cell phones or internet on Mars right now: http://spaceplace.nasa.gov/en/educators/mars_packing.pdf However, you might imagine that future explorers to Mars and those who develop a community there might put infrastructure in place on Mars that would allow for communications between people on Mars. You can read more about how cell phones and other communications devices work at: http://science.hq.nasa.gov/kids/imagers/ems/radio.html and http://www.fcc.gov/cgb/kidszone/faqs_cellphones.html and http://www.ccmr.cornell.edu/education/ask/index.html?quid=252 You can read about how we communicate between Earth and Mars at: http://mars.jpl.nasa.gov/msl/mission/communicationwithearth/