I have the T28 and it's a damn good phone.
The ONLY downfall is it's battery life... but ericsson knows this and that is why it has a Lithium-Polymer battery which you can charge at ANY time without damaging it. both Lithium-Ion and Lithium-Metal damages if you for example charge them when they're already half full.
So you can charge it whenever you can and you'll always have battery left, unless you go for a 4 day trip into the forest
Anyway that T28 also have the Chatboard and the Mp3-handsfree which both have very strong geek factor, I have both
And don't trust all the reviews... the first T28's had a software problem which was fixed a long time ago.
Anyway listen to what people that have the 8890 and the T28 think about it, and then make your choice, as I don't know anything about that 8890.
The only thing I know is that Ericsson also makes the base systems for mobile phones so I think they have a better understanding of the whole technology involved. I've usually gotten a better reseption at bad areas with my Ericsson then my friends has had with their Nokias (both on the same operator of course)
Also remember that the T28 world isn't a Triband phone it only has the 900 and the 1900 band.
My fingers hurt now so I'll stop writing
(edit) There is of course higher capacity batterys one which has 11h talktime I think

And the ultra slim that comes with it has a pretty decent talk time something like 2.5h but as already pointed out the stand by isn't very exciting (/edit)