For those of you with Verizon phones, you are in luck as South Korea is pretty much 100% CDMA-based. GSM phones like anything from AT&T and T-Mobile won’t work in South Korea no matter what they say unless you have a “world” phone that supports CDMA along with GSM.
To use your Verizon phone in South Korea, you will want to make sure you have the “International Dialing” feature in your plan, make sure you have it.
Second, you need to dial *228 on your Verizon phone and press 2 to obtain updated PRL prior to traveling to Korea! !MOST IMPORTANT!
This will work on EV-DO BlackBerry, EV-DO Treo, and any other EVDO Smartphone devices. (Most Android phones should work!)
Of course, don’t forget minutes are rather expensive at $1.99 per minute, which is ridiculous if you ask me. Of course, I am not sure if data is free. If it is, you can always use GoogleVoice to pay 5 cents per minute instead. (which what I do currently to call from my Nexus One from San Francisco to my mom in Korea)
Remember, in South Korea, they don’t have any pre-paid SIM cards like they do in other parts of the world. You can also “rent” a cellphone at the airport, which shouldn’t be too bad of an option but you might be missing data so plan accordingly if you are traveling to Korea soon.
If you can afford it (perhaps you can write it off as business travel expenses), you should make sure your phone can work before leaving.
For everyone else with another carrier such as Sprint, you will have to get rental phone there.
Also, if you are planning to stay in South Korea even longer (not a trip), perhaps permanently, read this blog post that shows you how to get your CDMA-based phone activated in South Korea. (if you love your phone but I would highly suggest to buy a new phone unless you just bought the Nexus One or somethin’)