CDMA is based on a proprietary standard mostly created by Qualcomm, an American semiconductor company.Having a phone that works on the correct standard is only half of the equation.Most of the world uses the Global System for Mobile Communications standard, better known as GSM.Europe mandated the standard in 1987 after a consortium and most countries adopted it. S., South Korea, and Japan — all of which use the CDMA standard.Choosing this strategy means that you'll have to rely on Skype, Whats App, or other internet calling (Vo IP) apps to make calls or risk being charged very expensive voice roaming fees.If your cell phone meets the hardware requirements, you'll have to decide between international roaming — which can get very expensive — or unlocking it to use a SIM card with a local number and prepaid service.International roaming allows you to keep your number from home, however, you'll pay each time that someone calls you or vice versa.Tip: When using a prepaid service in Asia, deactivate data roaming on your smartphone to avoid big, unexpected charges due to apps updating in the background.
Your cell phone will have to be tri-band or quad-band to work abroad — check the phone's hardware specs. Customers with Sprint, Verizon Wireless, and other CDMA carriers typically aren't able to join the local cell networks in much of Asia aside.
You can also try dialing *#06# to retrieve the IMEI.
Store the unique IMEI number somewhere secure (e.g., in an email to yourself).
T-Mobile is a popular choice with travelers in Asia because they offer free data roaming (allowing you to surf the web and make internet calls) without changing hardware.
You have to contact them to ensure that international data roaming is activated on your plan.SIM cards contain your local phone number, settings, and even store new contacts.