these are copy/pasted from threads... i'll try and summarize it at some point..
world phone: i have a tri-band gsm phone (nokia)
my carrier is att/cingular but you can get tmobile and there may be others.
roaming charges can be expensive ($1.30/min) ok in a pinch but for under $15 i buy local gsm cards from where i travel. all incoming calls are then free and long distance is significanlty cheaper (7 cents/min from thailand, 50 cents/min peru), the rates vary from country to country. local calls are as little as 2 cents /min and you can connect with locals, great for meeting people, dating, rendezvous etc. when i travel with friends we each get our own local numbers now we're connected no matter what and it makes it easier to split up and meet up- dirt cheap.
the important thing for me is that my phone works anywhere in the world that cells phone work except in a couple of countries that block it like cuba and myanmar.
oh and the trick is to get any gsm service from any provider here, it doesn't matter just get a gsm account. then go online and buy the least expensive gsm triband (world )phone you can find ( i really like the nokia's +/- $120) unless your provider offers a cheaper triband.
then google your phone model and 'unlock'. in 5 minutes and for $5.00 your phone will work with any gsm card.
you can also buy really inexpensive phones in places like thailand.
you got it. gsm phone has a replaceable chip , the gsm chip. this chip has all the phone number info for your phone to work. which ever card you instal, that's the number for your phone. no limitations. all you are doing is buying a cell phone number from a different carrier. your 'unlocked' tri band phone will be compatible with 99% of all the carriers and numbers in the wolrd.
the advantage is local rates wherever you maybe and phone that works everywhere there's a signal in case of an emergency.
The battery charger must be 'dual voltage'. It needs to operate on all voltages from about 110V to 240V and on frequencies between 50-60Hz.
The phone needs to be unlocked so it can operate with any SIM, anywhere in the world (we can unlock many phones for you)
Try and get a phone with a Lithium-Ion type battery
NOTE : You can only swap SIM cards if your phone is 'unlocked'
You can probably already guess the solution to this type of problem. Yes - buy yourself a new SIM and account from a local GSM service in the cities/countries you visit. This can be a very simple procedure if you buy a prepaid account. You don't have to fill out any paperwork or provide any credit checks or anything at all. You simply pay a moderate amount of money and in return get a SIM, a phone number, and a certain prepaid balance to be used for the cost of phone calls.
When you have spent the initial prepaid amount, you can buy additional time - perhaps paying by credit card via the phone, or perhaps buying extra time through phone shops. A new SIM card and phone number and account setup will typically cost somewhere between $10-30, and then you'll find that your local call costs are probably 20c-30c a minute - perhaps only one tenth of the cost of a US based service!
you should get a prepaid calling card, and then use this account any time you make an international call - from home, from work, and from your cell phone, too.
If you're going to be spending a reasonable amount of time in one country (ie if you'll be making a lot of phone calls!) then sometimes it is cheaper to have a local account as well as (or instead of) your HopAbroad account. For example, I use my HopAbroad account when casually/quickly traveling about Europe, but if I'm staying in Britain or Russia for a week or two, I then switch to a local account, where the costs to call locally within that country become very much lower. (Telestial http://www.telestial.com/)