said by cramer:
That used to be true, but with all the number porting these days, it's next to impossible to tell a number is "cell" just by looking at it. In the old days, you could look at an NPANXX and know what CO it's going to.
Iirc the FTC makes available a list of former landline numbers ported to wireless. There are other ways to make the determination as well using telco databases.