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Sources

• German, Kent. CNET. "SIM card explained." April 12, 2005. (Feb. 17, 2009)
  http://reviews.cnet.com/4520-10166_7-6160666-1.html
• GSM World. "GSM" (Feb. 17, 2009)
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• GSM World. "GSM Roaming." (Feb. 17, 2009)
  http://www.gsmworld.com/technology/roaming/index.htm
• OneSIMcard.com. "International Mobile Phone Rental Solution" (Feb. 17, 2009)
  http://www.onesimcard.com/?idmenu=3
• Reardon, Marguerite. CNET. "Verizon Expects 4G Launch Next Year." Feb. 18, 2009 (Feb. 23, 2009)
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• Rowell, David M. The Travel Insider. "Choosing the Best International Cell Phone Service for You." Dec. 3, 2008 (Feb. 17, 2009)
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• TigerTV. "What is GSM?" (Feb. 17, 2009)
  http://www.youtube.com/watch?v=OwaPm4JmhN0