Actually ...
Try a few searches on the
www.numberingplans.com website, that Przemolog first recommended to us
http://www.numberingplans.com/?page=...is&sub=phonenr
- mess around with the next 3 digits after the area code, eg the 555 of common examples - you will find provider information comes up for valid results, and some of these are mobile phone companies
I rather doubt that many companies would actually bother to keep and search such databases to determine tariffs or for any other reason, but it is hypothetically possible
Here are some of the 917 allocations you mentioned
http://www.numberingplans.com/?page=...ent_page=12288