Best option for world travelers and their cell phones?

Best option for world travelers and their cell phones?


Ok, from my research, there doesn't seem to be one good solution to this topic.


I have a tri-band phone (with a current Beijing CHINA UNICOM sim card). In Beijing, it's cheap to use. I wonder how it would operate in Shanghai, Hong Kong, or Taipei?


If I'm staying in these places for 1-2 months each, is it worth buying SIM card after SIM card in each place? Or is using the Beijing SIM card all the way the better option (of course, it would be more expensive)? But, what can I do here?


My second question is when I leave for America (after my trip in Asia comes to an end). I will, of course have the same phone (as it's TRI-band) (and probably a local SIM card from Asia). What would I do in America? And then in Mexico, after that?


What is the cheapest option for world travelers who only plan to stay somewhere for the short-term (a couple months but use frequent in/outband calling/and SMS messaging) and then move off again?

In the US T-Mobile is the only place I know of that offers SIM cards. Not cheap like HK and definitely more expensive than a regular mobile plan in US but good if you're just there a couple of weeks.