This is how I successfully imported my contacts from a Palm TX to the N900.
Please be aware there are probably many other ways to get the same result.
I suggest you to first try to use Bluetooth to send data between the devices.
It should be the easiest option, but for some reason it crashes my Palm device...

I hope this might help other Palm/Treo users upgrading to the N900, but please
understand I can't give you any guarantee at all that this will work for
you no matter what. As always, backup of your data, take care and enjoy!


Overview

I exported all my contacts in a single vCard file, converted the
charset to UTF-8 and imported directly into the N900 using the Contacts app.


Step-by-step instructions

1) HotSync

HotSync your Palm device to your PC using the HotSync Manager.

2) Export contacts from Palm Desktop into a vCard

I used Palm Desktop v. 4.2 for this, so the commands might be a bit different
for other versions. Overall, just select all your contacts and export them
as a vCard:

2.1) Open Palm Desktop
2.2) Choose the correct user at the top right corner
2.3) Click menu View -> Contacts
2.4) Category -> All
2.5) View -> Show Private Records (optional, of course)
2.6) Edit -> Select All (Ctrl+A)
2.7) File -> Export vCard (as "contacts.vcf", for example)

3) Optional step: convert character set

I'm from Brazil and several of my contacts have names or notes with accents or
special characters. Those accents and characters will be lost unless you
convert the charset of the vCard file to UTF-8. You can use many programs to
do this, but I'm using OpenOffice 3.1.1 for this example.

3.1) Open OpenOffice
3.2) Load the vCard file into OpenOffice
3.3) The "ASCII Filter Options" dialog should appear. Choose the correct
charset ("Western Europe (ISO-8859-1)", in my case)
3.4) File -> Save As
3.5) Select a different file name ("contacts-utf8.vcf", for example),
set "Save as type" -> Text Encoded (.txt),
check "Edit filter settings" and click "Save".
3.6) If asked, choose "Keep Current Format"
3.7) Set Character set -> Unicode (UTF-8), Paragraph break -> LF
3.8) Close OpenOffice and rename the file from .txt to .vcf if necessary

4) Copy the file to your N900

Use your preferred method to send the "contacts-utf8.vcf" file to
your N900 (into your Documents folder, for example)

5) Import the vCard file

On your N900, open the Contacts application. Click the menu ->
Get contacts -> Import contacts -> Import contacts file

This might take a while. It took almost a minute to import my contacts
(about 800), but everything seemed to be there!

The next step will be to merge SIM card and Skype contacts to the ones
imported. You can use the "Group" functionality of the Contacts app to
help you there.

6) Bugs and problems

I read that you might be able to import only 1024 contacts per vCard file:
https://bugs.maemo.org/show_bug.cgi?id=7192

I didn't experience this problem, but an obvious workaround if you have
more than 1024 contacts would be to repeat all steps as many times
as needed, exporting less than 1024 contacts each time.

7) Links

To get GVM/palm contacts into N900 contacts (using MS Outlook)

just migrated from PalmOS, with tips

wow, too many steps...

I tried to do similar with the Nokia PC Suite and it was some kind of hellish, because the Nokia PC Suite's "Communication Center" (calendar/contacts/etc. manager) doesn't seem to be able to handle vCard files with more than one contact in them. I ended up splitting them into individual vCard files and then importing all the individual files en masse. It worked just fine, though.

too long to read

I can confirm this works because i did it exactly the same way

it's good news for me. thanks.

so i only turned on Bluetooth on my palm and on the n900 and choose Kategory send on the Adressbook in my palm (Hagenuk palm OS 5.4.0)
Waited 1 min ( about 130 adresses) and´s done

Donjoe

@maemo55555@yahoo.cn, rsegerda@sina.com: the overview is just two lines, and should be enough for some. For the non tech-savvy, I tried to make the step-by-step as thoroughly as I could.

@Viqsi: I also tried using PC Suite for this, had the same problem (can only import one contact per vCard file). I thought about doing the same you did (creating individual vCards for each contact), but I wanted to create a "walkthrough" that most users could follow without downloading scripts or other tools.

@donjoe: I forgot about that option, thanks for sharing! It was one of the first things I tried, but it resets my Palm TX every time... But this is also not an option for older devices without Bluetooth.

This is the way it's supposed to work, and very easy. I've done this with my Palm as well as a number of phones, back in the N800 days. However, there was a problem with receiving full vcard files (as opposed to single-entry files) on the N900, at least with the previous firmware versions. I noticed that something changed (it's now possible to at least receive such files) with the latest upgrade but I haven't retried the above procedure yet - in the sense that I haven't actually imported the vcard file into contacts, I only saved it to file.

What happens when you do the above is simply that the Palm will transfer a file with name <category>.vcard (or possibly some other extension - it's been a while) to the N900. Very convenient.

Just transferred all contacts via bluetooth from my Treo 755P to my new N900 all 475 of them.
very painless.
Nice
now on to the Google Calender