The XDA II is the latest handet available but it does have a few drawbacks, Because it is a dual Handset ( data & Voice) you will have to decide which you will primarly use it for as there are different tariffs for both: (i.e.) Cheap data with expensive Calls or Cheap Calls with expensive data.
A friend of mine ran up a Bill of €3,000 in just one month by using it to collect e-mails because he was on a voice tariff..
The second issue I have with it is that you have to connect to collect emails which costs you each time, even though there may not be any emails to collect at that time ( money wasted)..
If you are looking for a PDA with windows CE then either a DELL axim of a compaq Ipaq, ( without any GSM/GPRS)
If you are looking for an orgainiser/ phone and email then i would really recommend Blackberry, because it used PUSH technology , this means that it will push any email to the device when it arrives on the server and you do not have to go looking for them, you can then reply to that email instantly. Best of all o2 offer a flat rate of €20 per month with unlimited email downloads etc... you can even browse the web on this unit..
I hope this helps