where can i find a free list of all US mobile/cell phone number?

Mobile phone providers are allocated numbers in "blocks," so potential
numbers will fall within the given range, barring number portability,
specialized numbers, forwarded numbers, etc.

It's unlikely, however, that such a list exists, and if it did, it
almost definitely wouldn't be made available to private parties.

If this is for telemarketing purposes, note that the Telephone
Consumers Protection Act (TCPA) puts restrictions on telemarketing in
general, and more so on lines where the called party pays, which would
include most mobile phones. The fines for violations can be very
steep, including $500 per violation (and one call may contain several
violations) to the receiver of the call, which can be tripled if it's
established that the violator willfully and knowingly violated the
TCPA, in addition to fines levied by the FCC.

I echo the cautions given by lisarea but would also like to say that I
have been involved in testing various telephone databases for more
than a decade and have never heard of what you are looking for.  I too
seriously doubt it exists and it certainly would not be free. 
Although phone lists are now less expensive, just a few years ago the
U.S. white pages could cost upwards of $50,000 from one of the Baby
Bells and that was just for the published numbers.

You can now buy such databases for relatively low cost but they
certainly don't contain cell phone prefixes.

In fact it might be a violation of law to posess such a list if you
had any intent of distributing it or even calling people on it.

A search on "NPA/NXX" should turn up info on which Wireless carriers
are assigned a certain block of numbers. Lists are available to the
carriers, but I do not believe they are free.