yes it may take 2-3 months...On the other hand, I was on the phone with AT&T the whole time when I had my discount removed, paid for the iPhone 3g, and then the rep on the phone put my discount back on.
I can see the discount already reflected on my account.
I just viewed my first bill online and it showed my corporate discount
my first bill was $75.33 (only 2 days prorated on my old plan) I think they overcharged me by .48 cents but it will give you guys a good idea on the amount of your bill. I'm an old customer so I pay behind instead of forward so no double bills. I have the 39.99 plan $30 data and $5 text and had 24 texts over (10c each) My corporate discount is 15%. Just pays for the taxes.
My corporate discount applies to both the voice and data on the iPhone 3G line...maybe everyones is different. My rate plan is like 34.xx per month, and I get like 5 bucks off if I do the unlimited text and data bundle.