FAQ - Cell Phone

Will my cell phone work in Vietnam?

Cell phone roaming in Southeast Asia isn't just possible, it's very easy to do!  Certain U.S. cellular phones will work in Southeast Asia, so if your phone meets a few conditions, you'll be able to call home on your own handset to tell the folks how your trip is going.  There is a catch - several of them, in fact.  You'll be able to use your phone only if:

  • Your phone uses the GSM cellular standard;
  • Your phone can access the 900/1800 band; and
  • Your phone's SIM can access the local networks - which means that
    • Your provider allows international roaming; or
    • Your phone is SIM-unlocked, allowing you to use prepaid SIM cards

Condition 1: Using the GSM Standard

Not all cell phone providers are created equal: in the U.S., digital cellular networks are split between GSM and CDMA.

U.S. operators using the GSM standard include AT&T (formerly Cingular) and T-Mobile.  Verizon Wireless and Sprint have been using the incompatible CDMA network.  CDMA-compatible phones won't be much use in a GSM-compatible country.  I understand that Verizon Wireless is now offering service using the GSM standard.  You will need to check with your cell phone provider if you are not sure.

Condition 2: Accessing the 900/1800 band

Outside the U.S., Japan, and Korea, the world's cellular phones use GSM technology.  However, the U.S.'s GSM networks use different frequencies than the rest of the world:  In the United States and Canada, GSM cell phones use the 850/1900 band - providers everywhere else use the 900/1800 band.

That means a dual-band GSM phone that works perfectly in Sacramento will be a brick in Singapore.  If you have a quad-band phone, that's another story: quad-band GSM phones work equally well on 850/1900 and 900/1800 bands.  European phones use the same GSM bands as those in Southeast Asia, so no problem there, either.

Once you have both issues settled, let's move on to your choices: using your current plan to roam internationally, or buying a prepaid SIM at your destination.  The pros and cons for each option will be laid out below.

Planning to roam with your cell phone in Southeast Asia?  Even if you have a GSM phone that can access the 900/1800 band, your cell phone may not always play well with local networks.  You have to check with your carrier if your contract allows you roam internationally, or if your phone is unlocked for the use of other carriers' SIM cards.

Option 1: International Roaming

Does your plan allow International roaming?  Check with your phone operator if you can use your phone in Southeast Asia, and what services you can use while you're roaming.  If you're a T-Mobile user, you can read T-Mobile's International Roaming Overview.  If your phone uses AT&T's network, you can find the info you need at their Roaming Packages page.

Be warned: it will cost you a lot more to make or receive phone calls while roaming abroad, assuming your phone does work at all, so don't be surprised if your phone bill has a few extra zeroes tacked on when you get back.

PROS: Use your own cellphone and get billed on the same account you use at home
CONS: Expensive, limited coverage

Option 2: Unlocked Phone, Prepaid SIM

If you have a quad-band GSM phone, but you think you're being stiffed by your provider on your roaming fees, you might also consider buying a prepaid SIM card in your destination country.

The SIM (Subscriber Identification Module or Subscriber Identity Module) card is unique to GSM phones, a transferable "smart card" that holds your phone settings and authorizes your phone to access the local network.  The card can be switched from one phone to another: the phone simply assumes the new SIM card's identity, phone number and all.  Prepaid SIM cards can be bought in every Southeast Asian country with GSM cellular service: simply buy a SIM pack, insert the SIM card into your phone (assuming it's unlocked - more on that later), and you're ready to go.

Prepaid SIM cards have a "load", or balance, included in the package.  This balance is deducted as you make calls on the new SIM; the deductions depend on the rates included with the SIM card you purchased.  You can "reload" or "top up" your balance with scratch cards from the SIM card's own brand, which can usually be found at certain convenience stores or sidewalk stalls.

Before you can use a local SIM card, though, you have to check if your phone is "locked" with your current provider.  Service providers often "lock" handsets, permitting only their SIM cards to use the phone.  This is done to prevent users from transferring their subsidized handsets to competing carriers.  However, if you're a longtime subscriber, your carrier might provide an unlock code if you ask nicely enough.

Check with the SIM card provider's homepage for each card's available services and call costs:

Prepaid Cell Phone SIM Cards in Southeast Asia - International Roaming
International Roaming - Using Prepaid Phone Cards
By Michael Aquino, About.com

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