I just got off the phone with a guy that got my 1500 SMS for $8.99 added (this was my 2nd time calling).
For those that are being told it's incompatible with the iPhone, the guy told me this as well when I first asked about it. I first of all said I had a coworker that had an iPhone 3G as well and it applied, and he just said he wasn't sure about them, but the system was telling him the code was incompatible with the iPhone plan. He mentioned something about the 200 SMS plan, but said it was the iPhone's unlimited data plan that was incompatible and of course you can't remove that. Since he mentioned SMS, I asked if he could just remove my 200 plan and add this in its place and he said it wasn't the SMS that it was incompatible with.. then he was like "wait a sec, maybe it IS the SMS plan and not the data" so he tried removing my 200 SMS messages for $5 and added this, and he said it went through and seemed surprised. He confirmed that I still had my unlimited data and now 1500 messages for $8.99, and I just logged into my account and verified it for myself.
So for anyone being told it's incompatible, be sure to specifically ask them to remove your current SMS plan and add that in its place.
I'm about to call back and try to get someone to add the U200 code as well
update: just talked to a woman that first of all asked me if it was noted in my account about the U200 code, and said that they can't just give out bonus minutes. Then she said to hold on a minute and said that she couldn't add it anyway because it was a grandfathered code that wasn't valid for new use so she couldn't add it anyway.
I'll probably try again later, but I'm almost scared to with hearing people saying they had codes show up on their account and then later disappearing... I don't know how much I want to tempt karma since I've already got my discounted 1500 SMS code on there, and I doubt I'll talk enough on the phone to need my full 450 anyway (plus the rollover minutes will help boost that every following month)