A reader asks: Is there any way to determine a person’s carrier given only their cell phone number? This would be useful if you wanted to send an email to your friend’s phone but only knew their phone number.
Answer: Thanks to number portability, this isn’t easy. In the old days, phone numbers were assigned in “blocks” to different carriers, so all you needed to know was an area code and the 3-digit exchange (the first 3 digits after the area code) to figure out which carrier the number belonged to. But number portability means that anyone can ditch their carrier and take their phone number to a new carrier, so the old “blocks” of phone numbers apportioned to each carrier are gradually being broken up.
However, there are a few sites that claim they can give you this information (for free) and a some other sources that will tell you for a fee.
Because of number portability, these sites are not necessarily going to be accurate.
For fee lookups (for businesses): MX Telecom Carrier Lookup
If you want to find all of the wireless carriers serving your ZIP code, try Wireless Advisor.
(page updated 3/9/2010)