You guys/gals: I posted a long post about how ATT determines eligibility upgrades. It's solid information how the process works.
1. First of all, it DOES NOT MATTER what your total bill is if you have a family talk plan. All it matters in a family talk plan is the primary line. All the secondary lines are not eligible for upgrades until usually month 20-21 unless one of those lines can generate more than $69.99 on its own (highly unlikely considering the second line usually only generates 9.99 plus $30 data). You could add misc stuff like ATT navigator and than maybe that secondary line will be eligible at month 18th (if that was the case you would have been eligible in dec 2010 and ATT would have moved your eligiblity date up 6 months. Again, it's HIGHLY unlikely the secondary line can generated $69.99 on it's own. You would be wasting a lot of money adding other features you really don't need.
So most people who purchased as secondary lines in June 2009, will be eligible for full upgrade subsidy on 02/2011.
To add further, regardless if you were the primary or secondary line (and if you had skipped the 3GS altogether). If the primary or secondary lines were eligible for full upgrades all the way up to Dec 2010, ATT would have moved your eligibility upgrade date to now eligible so you can order your iphone 4.
ATT does not count texting as part of it's calculations.
2. For individual lines, if you are on the cheapo 39.99 plan plus the $30 data plan, you won't be eligible for at least 18-21 months. This again excludes texting features.
If you are on a 59.99 plus $30 data plan, you will be eligible definitely at 18 months. So if you purchased in June 2009. You are next eligible on Dec 2010. However ATT was kind enough to move your eligibility up 6 months so you get to upgrade right now. But if you had waited till July 2009 to buy the iphone 3gS and had this 59.99 plus $30 data plan. Your eligbility date most likely was stuck at 01/2011.
I hope this info helps everyone still confused.