Having spent a lot of time in the FB world, this is probably against the Terms of Use.
http://www.facebook.com/terms.phpSpecifically, the following clauses:
"All content on the Site and available through the Service, including designs, text, graphics, pictures, video, information, applications, software, music, sound and other files, and their selection and arrangement (the "Site Content"), are the proprietary property of the Company, its users or its licensors with all rights reserved. No Site Content may be modified, copied, distributed, framed, reproduced, republished, downloaded, scraped, displayed, posted, transmitted, or sold in any form or by any means, in whole or in part, without the Company's prior written permission, except that the foregoing does not apply to your own User Content (as defined below) that you legally post on the Site."
And
"In addition, you agree not to use the Service or the Site to: ... use automated scripts to collect information from or otherwise interact with the Service or the Site"
On top of the legalese, the spirit of the Facebook Terms of Use is that people should have control over their privacy through FB, no matter where that information resides. Facebook would say, "What if someone changes their privacy preferences so that you're no longer allowed access to their phone number? Or what if they change numbers? Your data will at best be out of date and at worst violate their privacy."
Since Facebook offers no controlled mechanism for accessing phone numbers I think it's a safe bet that they don't want users exporting their friends phone numbers, no matter what.
YMMV, I guess, since Facebook is notoriously inconsistent in enforcing their terms of service.
