How do you distinguish if a US phone number is mobile or landline without any input from the phone number owner?

My company offers this website for free: http://www.IsItWireless.com It is number-portability aware; so it works even if someone ports their phone number to a different phone company.

Not to mislead you, you need to know I speak as a user not a technician. In America, all numbers are structured in the form xxx yyy zzzz. The xxx number is called the area code referring to the area of the country (state, county, city).Initially across America, the guy digits were a way to identify mobile numbers, called cell phones in America. The zzzz of the number was no more than an assigned number from an available pool of open numbers. Originally, the yyy was used to identify mobile service, and vendor of the service. As years passed, massive, rapid, growth, relaxed, changed rules, rethinking, people were allowed to switch service and vendors, and even state's and areas and keep their same numbers. As a result now it is virtually impossible to know. Personally, my first mobile was in Louisville, Kentucky, decades ago. When I bought a home in southern Kentucky, I decided to buy service in the new area and a new vender, and opted for complete new number, making it easier for me to get sequential numbers for all the members of my family. With the death of my wife and subsequent separation of the members of my family, I moved to Indiana and acquired a new service, vendor, mobile, and number. But also retained my old personal mobile and number from southern Kentucky, for a long period. I've recently moved to Asia and of course acquired a new mobile and vendor. Which permits me to point out another difference in countries. In America you must purchase your mobile and service  from the same vendor. Where I live now, you buy your mobile anywhere you wish, pick the vendor of choice, and they insert the chip with the number you wish from the pool of available numbers.

For sporadic, personal use, the LRN query form at the bottom of this page is useful:http://www.alcazarnetworks.com/data_services_lnp_lrn.phpThe “LINETYPE” parameter will tell you if it’s “WIRELESS” or “LANDLINE.”The “LEC” parameter will tell you which carrier owns the number.This is actually querying the LRN (Location Routing Number) database, which is how telco providers actually route calls and know which destination switch to send a call to, so it is accurate even in the case of numbers that have been ported to another provider.For higher-volume use, that site does offer an API. Pricing details are on that page.I’m not affiliated with that company, other than having used a few of their products over the years.