Making Sense of it All - Choosing the Right Phone For You!
GSM vs CDMA - Phone Frequencies
Wireless carriers in the United States operate over two different networks: Code Division Multiple Access (CDMA) and Global System for Mobile Communication (GSM). Though each technology transmits voice and data, they do so in different ways, which making a phone incompatible if you do not have the right plan. As a result, you can't take a CDMA phone and use it on GSM or vice versa. GSM phones can be taken to use in other countries as well (as long as the frequency is compatible - please see section below on dual band / tri band / quad band phones).
Verizon, Sprint, Nextel, Cricket and Alltel all operate using CDMA networks. The item description will say the CDMA carrier that the phone will work on. If the description says works for Verizon the phone will only work on the Verizon network, and the same for Sprint, Alltel, Alaska Wireless, etc.
Cingular, AT&T, T-Mobile, and Rogers Wireless and many other Global GSM Provider worldwide operate on a "GSM" network. If the phone specifically says "guaranteed to work with AT&T" for example, the phone is currently "locked" and will only work with AT&T and the same for T-Mobile and so on. These phones generally can easily be unlocked to be used with any GSM carrier that uses a sim card for a small fee (ranging from $8-$20) and the ability to unlock the phone depends on the model of phone you purchase.
GSM "Unlocked" Phones -
If the phone states "Unlocked" in the title and / or description you can just take out your sim card from your existing GSM phone and place it into another unlocked GSM phone. If the description says unlocked , you can use it on any GSM network worldwide. Only GSM phones can be unlocked so please look for the word GSM in the description. Also, you must make sure that the frequencies supported by the phone are compatible with your current wireless provider. Listed below are a few of the more popular carriers and the frequencies they operate on. You may just want to do a quick google search to see what frequency a specific phone / carrier operates on to assure you will have the clearest reception with your phone.
What does Dual Band and Tri Band mean? Or even Quad Band?
Where in The World can I use that phone!?
In America you need a phone that can operate on GSM 1900 MHz frequencies - this is the most common frequency in the Americas (800 Mhz and 850 MHz also work depending on your carrier) so most often a Tri band or Quad band phone is the best option. Dual band phones tend to work in the UK and Europe and most of the world (GSM 1800 and GSM 900).
Unlocked Vs. Locked Phones
Can my Verizon / Alltel / Sprint / Nextel phone be unlocked?
No, sorry... All the carriers mentioned above operate on CDMA networks and therefore can not be unlocked. Keep in mind that only GSM phones can be unlocked. Some CDMA phones are now dual compatible with GSM Sim cards in order to be used internationally, but for the most part CDMA phones can not be unlocked.
Can my AT&T / Cingular / T-Mobile / Rogers phone be unlocked?
Yes! Well for the most part. Most GSM phones can be unlocked. All the carriers mentioned above operate on GSM ntworks. All these wireless providers, provide you with a sim card upon activation. If you have an AT&T phone and you want to use your current service plan with another AT&T phone, all you have to do is take out your sim card and place it in the other AT&T phone and you can use the phone freel. If your phone uses a GSM Sim Card, it can be unlocked. Locking a phone is a carriers way to prevent its customers from switching over to phones with other carriers. Once a certain carrier has you, they do not want to let you go easily. Carriers also have deals with large cell phone manufacturers to make certain phone exclusive to them and they pay big $$$ to try and prevent people from easily being able to use their phones on other networks.
What Should I Look For? - The Nitty Gritty
Do I need a Smartphone / PDA Device?
Do you need the internet on your phone? Do you use email regularly? If you answered "yes" to either then, YES you do! Just keep in mind that with the Smartphones and PDA devices that you will need a data plan to go with them that supports the internet features of the phone and this can become pricey. I personally opted for the unlimited data plan on my Blackberry and it costs me about $50 a month. This is essential for me in order to answer customers emails in as short of time as possible.
...read the full guide with pics here