Before you unlock your phone, though, make sure it's compatible with the new carrier's network. Verizon and Sprint use a standard called CDMA, and AT&T and T-Mobile use GSM. GSM carriers place user information on a removable SIM card. CDMA Networks, store your information on the iPhone itself. How to tell if an iPhone is GSM or CDMA Most iPhones are GSM devices and it's really easy to tell. As long as there is a SIM slot the iPhone supports GSM Networks. If there isn't one then you are dealing with a CDMA iPhone.
These carriers will not work with your unlock phone:
Afghanistan
Afghan Telecom
Wasel
Algeria
Mobilis
Angola
Movicel (please contact your service provider to verify if the have switch to GSM)
Argentina
CoTeCal
Nextel
Aruba
MIO
Azerbaijan
Aztrank
Bangladesh
Citycell
RanksTel
Bermuda
CellularOne
M3 Wireless
Brazil
Nextel
Brunei Darussalam
B-mobile
Progresif Cellular
TelBru
Cambodia
Seatel
Cameroon
YooMee
Canada
MTS
Chile
WOM
China
China Telecom
Colombia
Avantel
Democratic Republic of Congo
Tatem Telecom
Denmark
Net 1
Dominican Republic
Tricom
Ecuador
CNT
Ethiopia
Ethiotelecom
Gambia
Gamtel
Georgia
Silknet
Ghana
Expresso Telecom
Gibraltar
Cts Mobile
Ghana
Expresso Telecom
Guam
Docomo Pacific
Iceland
Nova
India
MTS
Reliance
Indonesia
Smartfren
Esia
Iraq
Omnnea
Israel
Pelephone
Rami Levy Communication
Japan
NTT docomo
Au
SoftBank
Y!Mobile
eAccess
Disney Mobile
B-Mobile
Kazakhstan
Altel
Kenya
Flashcom
Popote
Kyrgyzstan
Fonex
Katel
Nexi
Sapat Mobile
Latvia
Triatel
Luxembourg
LOL Mobile
Macau
China Telecom
Madagascar
Telma
Malawi
Access Communications
TNM
Malaysia
U Mobile
Buzz me
FRiENDi Mobile
Telin Malaysia
YS mobile
Malta
Melita
Mauritius
MTML
México
Nextel
Moldova
Unité
Interdnestrcom
Mongolia
Skytel
G-Mobile
Morocco
Inwi
Myanmar
MPT
Ooredoo
New Zeland
Telecom
Spark
Slingshot
Skinny
Nigeria
Bourdex
Multilinks
NITEL
Odu'a Telecom
Starcomms
Visafone
Zoom
North Korea
Koryonlink
Northern Mariana Islands
Docomo Pacific
IT&E
Perú
Entel
Puerto Rico
Open Mobile
Romania
DigiMobil
Russian Federation
Sotel
Tula
Comstar
Sierra Leone
Sierratel
Slovenia
T-2
South Africa
Neotel
South Korea
SK Telecom
Olleh
LG U+
Sudan
Canar
Sweden
Net 1
Taiwan
Vibo
Tanzania
Sasatel
TTCL
Benson Informatics
MyCell
Egotel
Uganda
I-Tel
Ukraine
Intertelecom
TriMob
PeopleNet
United States
Affinity Cellular
Airlink
Appalachian Wireless
Armed Forces Wireless
Bendbroadband
Blue Wireless
Bluegrass Cellular
Boost Mobile
Breakaway Wireless
Bristol Bay Cellular
BZRMobile
C Spire
Carolina West Wireless
Cellcom
CellularOne
Chariton Valley
Chat Mobility
Chit Chat Mobile
Clear Talk
Convergence Technologies
Copper Valley Telecom
Credo Mobile
CTC Wireless
Custer Telephone
Defense Mobile (please contact Defense Mobile to verify, depends on your location)
Eco Mobile
Envie Mobile
Español Mobile
Expo Mobile
Family Talk Wireless (please contact Family Talk to verify, depends on your location)
Flash Wireless
FMP Comuunications
FreedomPop
Good2Go Mobile (please contact Good2Go to verify, depends on your location)
GreatCall
Infinium Wireless (please contact Infinium to verify, depends on your location)
Inland Cellular
Kajeet
Ketchikan Public Utilities
Madstar Mobile
Matanuska Telephone Association
Mid-Rivers Wireless
nTelos
Nemont
Net10 Wireless (please contact Net10 to verify, depends on your location)
NetZero
Northwest Missouri
OTG Mobile (please contact OTG Mobile to verify, depends on your location)
Page Plus Cellular
Pioneer Cellular
Pix Wireless
Project Fi (please contact Project Fi to verify, depends on your location)
Proven Wireless (please contact Proven Wireless to verify, depends on your location)
Puppy Wireless
Ready Mobile
Red Pocket (please contact RedPocket to verify, depends on your location)
Republic Wireless
Ring Plus
ROK Mobile (please contact ROK Mobile to verify, depends on your location)
Sagebrush Cellular
Select Wireless
Scratch Wireless
Reliance Cdma Phone Price
Speed Talk Mobile
Sprint
Unlock Cdma To Gsm
Sprocket Wireless
Straight Talk (please contact Straight Talk to verify, depends on your location)
Strata Networks
S & R Communications
Tempo Telecom (please contact Tempo Telecom to verify, depends on your location)
TextNow
Thumb Cellular
Ting (please contact Ting to verify, depends on your location)
Gibraltar
Cts Mobile
Ghana
Expresso Telecom
Guam
Docomo Pacific
Iceland
Nova
India
MTS
Reliance
Indonesia
Smartfren
Esia
Iraq
Omnnea
Israel
Pelephone
Rami Levy Communication
Japan
NTT docomo
Au
SoftBank
Y!Mobile
eAccess
Disney Mobile
B-Mobile
Kazakhstan
Altel
Kenya
Flashcom
Popote
Kyrgyzstan
Fonex
Katel
Nexi
Sapat Mobile
Latvia
Triatel
Luxembourg
LOL Mobile
Macau
China Telecom
Madagascar
Telma
Malawi
Access Communications
TNM
Malaysia
U Mobile
Buzz me
FRiENDi Mobile
Telin Malaysia
YS mobile
Malta
Melita
Mauritius
MTML
México
Nextel
Moldova
Unité
Interdnestrcom
Mongolia
Skytel
G-Mobile
Morocco
Inwi
Myanmar
MPT
Ooredoo
New Zeland
Telecom
Spark
Slingshot
Skinny
Nigeria
Bourdex
Multilinks
NITEL
Odu'a Telecom
Starcomms
Visafone
Zoom
North Korea
Koryonlink
Northern Mariana Islands
Docomo Pacific
IT&E
Perú
Entel
Puerto Rico
Open Mobile
Romania
DigiMobil
Russian Federation
Sotel
Tula
Comstar
Sierra Leone
Sierratel
Slovenia
T-2
South Africa
Neotel
South Korea
SK Telecom
Olleh
LG U+
Sudan
Canar
Sweden
Net 1
Taiwan
Vibo
Tanzania
Sasatel
TTCL
Benson Informatics
MyCell
Egotel
Uganda
I-Tel
Ukraine
Intertelecom
TriMob
PeopleNet
United States
Affinity Cellular
Airlink
Appalachian Wireless
Armed Forces Wireless
Bendbroadband
Blue Wireless
Bluegrass Cellular
Boost Mobile
Breakaway Wireless
Bristol Bay Cellular
BZRMobile
C Spire
Carolina West Wireless
Cellcom
CellularOne
Chariton Valley
Chat Mobility
Chit Chat Mobile
Clear Talk
Convergence Technologies
Copper Valley Telecom
Credo Mobile
CTC Wireless
Custer Telephone
Defense Mobile (please contact Defense Mobile to verify, depends on your location)
Eco Mobile
Envie Mobile
Español Mobile
Expo Mobile
Family Talk Wireless (please contact Family Talk to verify, depends on your location)
Flash Wireless
FMP Comuunications
FreedomPop
Good2Go Mobile (please contact Good2Go to verify, depends on your location)
GreatCall
Infinium Wireless (please contact Infinium to verify, depends on your location)
Inland Cellular
Kajeet
Ketchikan Public Utilities
Madstar Mobile
Matanuska Telephone Association
Mid-Rivers Wireless
nTelos
Nemont
Net10 Wireless (please contact Net10 to verify, depends on your location)
NetZero
Northwest Missouri
OTG Mobile (please contact OTG Mobile to verify, depends on your location)
Page Plus Cellular
Pioneer Cellular
Pix Wireless
Project Fi (please contact Project Fi to verify, depends on your location)
Proven Wireless (please contact Proven Wireless to verify, depends on your location)
Puppy Wireless
Ready Mobile
Red Pocket (please contact RedPocket to verify, depends on your location)
Republic Wireless
Ring Plus
ROK Mobile (please contact ROK Mobile to verify, depends on your location)
Sagebrush Cellular
Select Wireless
Scratch Wireless
Reliance Cdma Phone Price
Speed Talk Mobile
Sprint
Unlock Cdma To Gsm
Sprocket Wireless
Straight Talk (please contact Straight Talk to verify, depends on your location)
Strata Networks
S & R Communications
Tempo Telecom (please contact Tempo Telecom to verify, depends on your location)
TextNow
Thumb Cellular
Ting (please contact Ting to verify, depends on your location)
Total Call Mobile
TotalWireless
TotoWireless
Touch Mobile
TracFone (please contact TracFone to verify, depends on your location)
UWT Mobile (please contact UWT Mobile to verify, depends on your location)
Verizon
Virgin Mobile
Voyager Mobile
ZingPCS
Vietnam
S-Fone
Uzbekistan
Uzmobile
Perfectum
Yemen
Yemen Mobile