brinked - 10:45 pm on Jun 11, 2012 (gmt 0)
I don't think having a phone number displayed prominently would be a ranking factor. I think if google does in fact use having a support number as a factor, it can be found anywhere on the site so long as it can be easily found by a user.
A lot of great sites that offer wonderful support dont display their number prominently. Having it on a contact or support page is more than enough.
Even if a legit business has the phone number displayed in an image in the header, why would they not also list that same number on a support/contact page in a readable format? How many support pages list their support number in an image? That would be silly.