Why won't it let me do a standard upgrade on anything but an iphone?

I am out of my 2 year contract.  I want to do a standard upgrade and not the installment next upgrade.  When I go to upgrade my phone, it will only let me do a standard upgrade with an iphone and no other smart phone.  I've talked to numerous AT&T support personnel and they keep transferring me to someone else telling me it is not their department.  They've even put in a support request for me and I get the response that it's not their area and refers me back to the people that sent me to them.  They have told me that I am eligible for an upgrade, but don't understand why it will only allow me to get an iPhone with a standard upgrade and not any other smart phone.  Has anyone else had this problem?  AT&T doesn't seem know how to fix it so I am hoping someone here does.