CDMA phone in Vietnam?

Only in America..?

An accurate analogy might be the 110/220 volt power problem,
too, only in America...

The rest of the world use GSM  (Global - key word)

G.   Good luck!

CDMA is either completely extinct, or close to it here, so (in lieu of a solid answer) let me offer up this advice:

Take your phone to one of these stores:

Thegioididong

There probably won't be anyone that speaks English (see Customer Service thread) and they'll probably act like the effort is killing them (ditto), but just be nice and have "CDMA/GSM?" written out beforehand, or try your luck with Google Translate.  Their techs (or their greeter) might be able switch it over to GSM on the spot, if it's truly unlocked.

One other thing - don't let the phone out of your sight, even with the most reputable companies, or you may find yourself holding a iPhone 4 in the shell of your 6s.

Teacher Mark wrote:

CDMA is either completely extinct, or close to it here, so (in lieu of a solid answer) let me offer up this advice:

Take your phone to one of these stores:

Thegioididong

There probably won't be anyone that speaks English (see Customer Service thread) and they'll probably act like the effort is killing them (ditto), but just be nice and have "CDMA/GSM?" written out beforehand, or try your luck with Google Translate.  Their techs (or their greeter) might be able switch it over to GSM on the spot, if it's truly unlocked.

One other thing - don't let the phone out of your sight, even with the most reputable companies, or you may find yourself holding a iPhone 4 in the shell of your 6s.

This would be the best advice I have read: anywhere

Teacher Mark wrote:

One other thing - don't let the phone out of your sight, even with the most reputable companies, or you may find yourself holding a iPhone 4 in the shell of your 6s.

He should be so lucky because that iPhone 4 would be GSM and would work in Vietnam and that CDMA phone never will.  I'm no engineer but I think the differences are pretty deeply rooted in the phone structure and how it handles data.  If there was a software fix that a store could do, people in the US would  be switching back and forth between Verizon/Sprint and AT&T/TMobile all the time with the same phones.

If you are still in the US, put your 6S on Craigslist and use the proceeds to buy an unlocked GSM one.  Since the 7 comes out soon, Apple will be selling the new 6S at a discount.

If you happen to experience trouble connecting to services while traveling, follow steps below.

1.Verify the device is not in “Airplane Mode”.  Then, power the device off and back on.  This will force your device to re-register with the roaming partner. 

2. Ensure the device is set to allow roaming: Settings > Cellular > Roaming > Voice
Roaming and/or Data Roaming (Set to on)

3.) Manually  change  the  device  mode:  Settings  >  Cellular  >  Roaming  >  toggle
International CDMA to OFF (upon returning to U.S. device will need to toggle back ON)

4.Manually select a carrier: When device is in GSM/UMTS mode 'Carrier' will appear in the Settings menu > Tap on Carrier and toggle Automatic to OFF to allow for manual selection of GSM carriers > Select an available carrier

Sprint Iphone 6s

I hope Teacher Mark is correct.  I do know that my brother who lives in NY and travels to Europe frequently has a Verizon phone and told me that he could make it work there but I never really got into the how of it.