wow, I hoped, but didn't expect that someone actually listens to my tiny voice in the vacuum of the great Interspace. :)
I honestly do highly appreciate that, it's a really great move by you and I'm grateful that you care about perfecting your product :)
Most companies think they cannot afford listening to their users, those who do earn my deep respect.
Btw. I'm from Germany and "mobile phones" can be differentiated easily here. Not only that, you'll even know which network the other number is signed up with.
D1 T-Mobile: 0151x, 0160, 0170, 0171, 0175
D2 Vodafone: 0152x, 0162, 0172, 0173, 0174
E-Plus: 0157x, 0163, 0177, 0178
O2: 0159x*, 0176, 0179
Locating positions of landlines phone numbers is even easier, because there are databases. The picture in the german wikipedia article explains how the association with a location works (no need to read the entire article). http://de.wikipedia.org/wiki/Telefonvorwahl But here you can get a free Database containing all landline numbers: http://www.vorwahl-nummern.de/vorwahlen/download.php
In the US, thankfully, pro-consumer laws require telcos and wireless carriers to let you take your number. With some restrictions, a number from anything can end up on anything.
So no, not possible to detect using rules. It is possible using a telco routing lookup.
You cannot know the carrier because you can keep your number when changing them. I'm with Vodafone and have a 0176 dialing code carried over from my previous contract. But as others pointed out, in the US mobile numbers get normal landline dialing codes so you cannot see a difference.
So, in a way, yes, it's possible for some customers to automatically detect that, but then you need to question how many of them come from countries where there is a difference and whether it's really a good use of your time and money to implement something that might only benefit a percent of your users. As for me, even though I'm conscious of UX, I wouldn't care much if I had to classify my phone number once. What they described in the article already goes way beyond what most other signup forms do.
(Fun fact regarding area codes and figuring out a city from that: The village I lived in previously was pretty much halfway between two smaller cities and it had the area code from one but administratively belonged to the other. So not even that is easy ;-))
I'm not sure about this in a world with number portability.
> email address and website url are differntiatable too
Yep, we do this already.
> auto-import feature LinkedIn/Facebook/Google, that searches for the contact's
We'd like to pull in social data. It's not trivial, though services like FullContact.com can help.