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In the U.S., the service providers-Cingular, Sprint, T-Mobile and Verizon-largely control the phones you can use on their networks. So before you get your heart set on a specific model, consider what the carrier will bring to the table.

VOICE
There are two voice networks: CDMA (Verizon and Sprint) and GSM (T-Mobile and Cingular). There is no inherent difference in quality between the two, but GSM phones store your contacts and service info (though not applications) on a removable SIM card, which means that upgrading devices or switching between a workday smartphone and a more portable weekend phone is a breeze-just swap the SIM.

DATA
All of the carriers have data networks with speeds similar to a home dial-up connection. But CDMA is
further along in rolling out the next generation of data connectivity, which will bring broadband-like speeds. Verizon already offers its high-speed network, EV-DO, in 30 cities, and Sprint will officially launch EV-DO service later this year. Cingular is about a year away from fully deploying the GSM equivalent network, known as UMTS.
(T-Mobile hasn´t yet announced its plans.) In addition to significantly faster browsing, these high-speed networks make it possible to get smooth streaming video and audio.

CARRIER BREAKDOWN

CINGULAR
The Good: Uses SIM card, has â€rollover
minutes,†wide coverage, lots of smartphones
The Bad: High-speed network
currently limited to six markets
Frequencies and Networks: 850/1,900MHz GSM; GPRS, EDGE, UMTS
Data Pricing: From $20/month, for 5 MB,
to $80/month, for unlimited data
Smartphones: Audiovox SMT5600,
Motorola MPX220, Nokia 6620, Nokia
N-Gage QD, Siemens SX66, Treo 600, Treo 650

SPRINT
The Good: Pay-as-you-go data for light users
The Bad: High-speed network
not widely available until early 2006
Frequencies and networks 800/1,900MHz CDMA; 1xRTT, EV-DO
Data Pricing: 1/K for pay-as-you-go; $20/ month for non-PocketPC devices and $35 for PocketPCs, for unlimited 1x data and messages
Smartphones: Audivox PPC-6600, Samsung i500, Samsung i600, Treo 600, Treo 650

T-MOBILE
The Good: Wide range of devices, cheap data, easy data roaming in Europe; Wi-Fi-enabled devices can switch seamlessly to T-Mobile Wi-Fi hotspots
The Bad: No official upgrade plan to UMTS, limited rural coverage
FrequencY and networks 1,900MHz GSM; GPRS, EDGE
Data Pricing: $30â€$80/month, for unlimited data, depending on device
Smartphones: HP6315/6310, Nokia 3660, Nokia N-Gage QD, Treo 600

VERIZON WIRELESS
The Good: High-speed data network has the best coverage
The Bad: Typically slow to adopt new phones, expensive Frequencies and networks 800/1,900MHz CDMA; 1xRTT, EV-DO
Data Pricing: Plans range from
$30/month, for 5 MB of 1xRTT data, to $80/month, for unlimited EV-DO data
Smartphones: Audiovox XV6600, Samsung i600, Samsung i700, Treo 600

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