Give them time. Over the last week, AT&T seems to have been slowly moving up peoples' upgrade date. Mine was originally in November, but was moved to "now" over the weekend. If you're lucky, they'll get around to you, soon.
On the other hand, I am in a similar situation: we have a family plan, and my wife and I got our 3GS's on launch day last year (at the same time). However, I'm eligible, but her phone is still listed as being in February. I'm still lost as to how two phones bought at the same time can have two different eligibility dates (this was still true before AT&T moved up the dates -- the original dates were November and February, and the dates are now "now" and February).