The P990i is still a little buggy but stable. Though there are less 3rd party applications on it, but all that you need for a business phone is there... schedule, phone functions, opening Word, Excel, pdf documents, camera, etc.
If you are looking for a serious business phone, then the P990i is a contender. If you are looking for a PDA phone that you would not mind little problems here and there, but want to download a load of 3rd party apps, then go for the Dopod... good luck with the Dopod.
If you are looking for a business phone that is stable, has reasonable amount of 3rd party apps, sounds great as a phone, does email with Blackberry support, opens Word, Excel, PDF files, keeps your schedule, sync with both PC and Mac, then you might want to look at the Treo 650 or the newer 750. So far this is the most solid business phone I have ever used.
Did I mention FAST as well? The P990i is slow. Maybe SE will fix that with firmware updates. So its up to you really... go test the P990i and see if you can stand the speed of the phone. The same problem is with the M600 as well... Symbian 9 is slow... painfully slow...
I will never part with my money on the Dopod. Hell, I will not use it even if I get it for free... I know many others will... but I really cannot trust the M$hit operating system no matter what they say.
The above are my personal opinion and preference. In no way this is meant to offend any Dopod fans or Windows Mobile user. After going through all the PDA phones in the market without a budget in mind, I still settled for the Treo. After sales service is still one of the best in the market.
SE990i - got a few friends using, say very slow and some area receiption no good.
Dopod - design is fantastic but function wise not stable (thats what i heard).
Treo650/750 - design is so-so and some say ugly but function wise is the best, I use the 650 for 2 years and no hardware problem, fast, reliable, one-hand sms and call. Hope Treo would employ some top class product designer for their next phone...
Treo 750v doesnt have any form of Wifi, not even with wireless SD cards via SDIO i last heard.
the 838 Pro is not too bad actually. tried one myself, and it's working fine. but honestly, still prefer the older WM2003, due to speed. WM5 looks cooler, but slower =(
P990i is also ok. but as a seasoned WM user, Symbian 9 dont look too user friendly to me... and not to mention the keyboard flap feels cheap and looks like it'll break sooner or later...
of course P990i is a smaller phone overall, but comes with a big trade off. the keyboard is fingernail accessible to me... Dopod's 838Pro has a REALLY nice keyboard, and a keyboard on phone that i actually used for once... =)