I am using GSM system more compatible and roaming capability if i travel otside my country. CDMA is used by limited countries such as: US , China, Korean .....

Mine is tmobile.. so GSM. When I was in alaska, I was surprised that my phone worked!

using gsm technology is the right choice at this time. gsm has capability to roam between one operator to others between one country to anathor country bcoz this technology is built based on global standarisation around the world.
Almost every contry currently use this system for the cellular:
http://www.gsmworld.com/roaming/gsminfo/index.shtml

CDMA i think it is better on voice quality but we are stuck if we travel outside the operator coverage. there is few limitation such as thing like roaming as GSM. also in GSM we can just carry the simcard everywhere and change our handset wherever we like. Ithink 3 bigest GSM operator in US are tmobile, cingular and at&t.
as http://www.gsmworld.com/
big operator using CDMA are verizon and sprintpcs. http://www.cdg.org/index.asp

Korea is CDMA heaven

Korea is the first country whose operator meet criteria for 3G; data rate meet 384 kbps for downstream, but not using UMTS/WCDMA but using CDMA technic .

I have no clue about my phone..., but I'm in Korea, so probably CDMA

if you have simcard attached somewhere with your cellphone normally inside the battery slot then most probably GSM if not it might be CDMA. Korea is CDMA heaven yet SK telkom has GSM network too.
gsm simcard: