The only downsides to posting your phone number in the member area are:

(a) getting calls that are really general tech-support issues that don't relate to problems with your site

(b) getting old guys calling who are obviously jerking off while talking to you and asking all sorts of nasty detailed questions about the models.... and sometimes about you personally (AJ gets "You sound cute" on the phone all the time)

(c) People are completely clueless and will call you at 4AM or 6AM or other inopportune times.

(d) People who aren't quite all there that will call multiple times in a row and ask the same questions because they have memory loss.

(e) Nice guys who are lonely and as soon as they figure out there's someone they can talk to, they will call a bunch of times.

We have had all of the above at one time or another.

If you can be graceful and subtle on the phone, you can get rid of most of the pesky people fairly easily without offending them, but there will be a few here and there that just don't "get it" and you'll probably have to be somewhat rude to get rid of. I question whether the benefit (or perceived benefit) is really worth the effort you'll put into it, but I applaud the effort to provide a personalized experience for the member.