Picking Out an 'Unlocked' Smartphone
The first question you may be asking is what exactly is an "unlocked" smartphone? The second is probably "Why should I care?"
The answer to the second question is that you could save hundreds of dollars per year on your phone bill by using an unlocked phone on a smaller carrier. The first question is a bit more complicated.
If you're like most Americans with a smartphone, you probably have an Apple or Android device that you got for free (or less than $200) when you signed a two year contract with one of the "Big Three" American network providers.
These providers subsidize an expensive phone for you, and in return you are obligated to pay their (costly) monthly talk and data fees.
An unlocked phone is one that is not tied to any carrier and thus can be activated for a much cheaper monthly fee, or pay-per-minute prices.
Note that this is different from "jailbreaking" (iPhone) or "rooting" (Android). That process is used to gain access to the administrator account of your phone and lets you make changes to the software or installed apps that are not approved by Apple or your carrier.
GSM vs. CDMA.
Go to ebay, amazonwireless.com, or any number of sites and you'll quickly become overwhelmed by the number of options and range of prices.
Here is a quick run-down of what to look for in an unlocked phone.
1. CDMA vs. GSM. These are two competing technologies that are wholly incompatible with each other (a CDMA phone cannot be used on a GSM network, and vice versa.)
CDMA stands for Code Division Multiple Access. This is the technology used by Verizon and Sprint in the US and few other places.
GSM stands for Global System for Mobile Communications. It is used by AT&T and T-Mobile in the US and nearly everyone else in the world. GSM phones use a SIM Card, a card provided by your carrier that can be switched between phones and controls your access to network features like talk, text, and data.
There are many carriers that offer inexpensive monthly fee's if you have an unlocked phone, but we will focus on T-Mobile and Walmart's Straight Talk, since they are currently two of the most popular here in the US. They also both happen to use GSM technology.
So to get the cheaper monthly rates of those two carriers, you need an unlocked GSM phone, buy a SIM card and away you go. Unfortunately it is not that simple.
Differing Frequency Bands
There are several frequency bands commonly used by GSM phones, including 850, 900, 1700, 1800, 1900, & 2100MHz. Obviously the more bands your phone supports the more versatile, but below is a breakdown of what each band is used for.
850MHz 1900MHz
This band is used for talk, text and 2G (EDGE) data on AT&T, Straight Talk, & T-Mobile, as well as several foreign carriers. AT&T & Straight Talk also use this bandwidth for their 3G networks.
The terms of AT&T's failed take-over/merger with T-Mobile requiered them to give the smaller carrier a chunk of this bandwith. As a result, T-Mobile is now rolling out HSPA+ (4G) on this bandwith, mostly in large to midsize cities. Check an unofficial coverage-map to see if you are covered.
1700MHz and 2100MHz (also known as AWS).
In the US, these frequencies are used only by T-Mobile and a few regional carriers (like Cincinnati Bell).
A phone must access both to utilize HSPA+ (3/4G) on T-Mobile (1700MHz band sends data, and the 2100MHz band recieves data).
900MHz and 1800MHz
These bands are used internationally.
Summary
A phone supporting only the 850/1900MHz bands will work for AT&T/Straight Talk talk, text & 3G. It will also work for T-Mobile Talk, Text, and 2G, as well as 3/4G in some locations.
A phone supporting 850/1900/1700/2100 will work with all T-Mobile Services.
Sources:
http://www.timeatlas.com/cell_phones/prospect/defining_a_world_phone#.UPXFrrt5UeM
http://reviews.cnet.com/2719-3504_7-287-4.html
www.straighttalk.com
http://support.t-mobile.com/docs/DOC-4988
The answer to the second question is that you could save hundreds of dollars per year on your phone bill by using an unlocked phone on a smaller carrier. The first question is a bit more complicated.
If you're like most Americans with a smartphone, you probably have an Apple or Android device that you got for free (or less than $200) when you signed a two year contract with one of the "Big Three" American network providers.
These providers subsidize an expensive phone for you, and in return you are obligated to pay their (costly) monthly talk and data fees.
An unlocked phone is one that is not tied to any carrier and thus can be activated for a much cheaper monthly fee, or pay-per-minute prices.
Note that this is different from "jailbreaking" (iPhone) or "rooting" (Android). That process is used to gain access to the administrator account of your phone and lets you make changes to the software or installed apps that are not approved by Apple or your carrier.
GSM vs. CDMA.
Go to ebay, amazonwireless.com, or any number of sites and you'll quickly become overwhelmed by the number of options and range of prices.
Here is a quick run-down of what to look for in an unlocked phone.
1. CDMA vs. GSM. These are two competing technologies that are wholly incompatible with each other (a CDMA phone cannot be used on a GSM network, and vice versa.)
CDMA stands for Code Division Multiple Access. This is the technology used by Verizon and Sprint in the US and few other places.
GSM stands for Global System for Mobile Communications. It is used by AT&T and T-Mobile in the US and nearly everyone else in the world. GSM phones use a SIM Card, a card provided by your carrier that can be switched between phones and controls your access to network features like talk, text, and data.
There are many carriers that offer inexpensive monthly fee's if you have an unlocked phone, but we will focus on T-Mobile and Walmart's Straight Talk, since they are currently two of the most popular here in the US. They also both happen to use GSM technology.
So to get the cheaper monthly rates of those two carriers, you need an unlocked GSM phone, buy a SIM card and away you go. Unfortunately it is not that simple.
Differing Frequency Bands
There are several frequency bands commonly used by GSM phones, including 850, 900, 1700, 1800, 1900, & 2100MHz. Obviously the more bands your phone supports the more versatile, but below is a breakdown of what each band is used for.
850MHz 1900MHz
This band is used for talk, text and 2G (EDGE) data on AT&T, Straight Talk, & T-Mobile, as well as several foreign carriers. AT&T & Straight Talk also use this bandwidth for their 3G networks.
The terms of AT&T's failed take-over/merger with T-Mobile requiered them to give the smaller carrier a chunk of this bandwith. As a result, T-Mobile is now rolling out HSPA+ (4G) on this bandwith, mostly in large to midsize cities. Check an unofficial coverage-map to see if you are covered.
1700MHz and 2100MHz (also known as AWS).
In the US, these frequencies are used only by T-Mobile and a few regional carriers (like Cincinnati Bell).
A phone must access both to utilize HSPA+ (3/4G) on T-Mobile (1700MHz band sends data, and the 2100MHz band recieves data).
900MHz and 1800MHz
These bands are used internationally.
Summary
A phone supporting only the 850/1900MHz bands will work for AT&T/Straight Talk talk, text & 3G. It will also work for T-Mobile Talk, Text, and 2G, as well as 3/4G in some locations.
A phone supporting 850/1900/1700/2100 will work with all T-Mobile Services.
Sources:
http://www.timeatlas.com/cell_phones/prospect/defining_a_world_phone#.UPXFrrt5UeM
http://reviews.cnet.com/2719-3504_7-287-4.html
www.straighttalk.com
http://support.t-mobile.com/docs/DOC-4988
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