That sounds like two separate UI bugs.

1. Merging should probably ask for confirmation.
2. The warning could be better, assuming it really means it will only delete the exact information.

And a feature request:

3. Some way to unmerge, please.

Based on this thread, this strikes me as a rather desirable bug/feature request, depending on your point of view:

4. Backup then restore should get you back to where you were before - or at least have that potential. That means "delete all contacts" should, at the worst, only delete those contacts which are actually on the phone at the time, not contacts which haven't yet been synced to the phone.

And this would be a nice bonus, letting you confidently explore with the phone by limiting possible damage:

5. General undo facility to undo configuration changes including contact changes would be great! C'mon guys

This is one of the reasons why I think the whole contacts integration with all your IM services isnt up to snuff yet. I'm just glad there are alternatives (Pidgin for ex.) that allow you to connect to a wide variety of networks. I hope the makers of Fring come out with a maemo 5 version so that we also get video skype call support they just brought over to s60.

see (and possibly vote for) this enhancement request

Yes, I am rather uncomfortable with putting any IM contacts into the N900 address book because of this revelation, so I'll probably be looking for another app to handle IM on it if isn't resolved.

I definitely want to IM on the N900 - so that clients think I'm a really hard worker because I'll be always online . But this issue, I understand how it's arisen, but it's very concerning.

The "warning" isn't informative enough, among other things. When you get a warning that it'll delete all contacts, it's not obvious what it means because there are several different things that could mean.

It's a mistake, of course, but natural to hope it's not too dangerous - for the simple reason that adding IM contacts and removing IM contacts from the phone list should be complementary operations - that is, do the opposite of each other.

If you remove an IM contact from your phone's contact list, it doesn't usually mean you want to remove your connection to them from your IM account. It just means (I would normally expect) that you don't want it in your phone's contact list any more.

Btw, does anyone know a way to collect all IM contacts from all different services used and back them up in a safe place, regularly? With ability to restore individually and all together? By that I mean not having to do a long-winded web operation with umpteen different web sites to make a backup.

You could always write them down on a piece of paper. Or a word-type document.

Well, honestly, the quality on Pidgin isn't much better than the contacts app in the N900. And you will still delete contacts from the servers if you delete them in Pidgin.

The problem is that people aren't thinking, "this is an IM chat client like Pidgin," they are thinking, "This is a mobile phone with a phone book, just like my other mobile phones," but it isn't, it is much more "connected" than that. If you carry on an e-mail conversation with someone in GMail, suddenly their status will start appearing in your N900's contact list!

I agree with jjx, what is needed here is some more guard rails and seat belts. You need to be able to undo changes that you make to your contacts without much hassle, and you need more confirmation dialogs with more clearly worded warnings.

Can't we request a feature that can set ''Delete original contacts'' so you can decide yourself if you keep them or not?
And I don't know if this has been mentioned but in MSN you can see a list of contacts that have you in their list in Tools>Options>Privacy

I agree with both of the above. It's a surprise because it's not what phone contact lists have traditionally done.

In particular, some other mobile phones let you add and remove IM contact information from their main contact list, but that doesn't affect the server list. That's because it's no different from adding and removing email addresses and phone numbers.

A lot of people even like to maintain different lists on their phone then, say, their computer address book or paper address book of all known contacts.

I expect people who are used to syncing their phone contacts with their big database on Google or on their main computer, and who always aim to have One Big List(tm) on all devices, will not be as surprised.

But they might still be surprised, if they're not used to thinking the IM client way.

After all, if you delete info and then sync, often deletions are synced around too. That said, you usually have some control over this - whether it's dialogues at sync time saying "do you want to delete the following contacts removed from $DEV1 and still present on $DEV2?", or an option to sync in one direction only.

So even regular syncers can correct their mistakes that way.

A lot of people don't sync their phone contact list regularly with other systems. They just maintain the list manually, or bluetooth entries around. They're not expecting deletions to propagate.

Culture clash, I guess, between the way people maintain phone numbers on their phones (and have done forever), and the way IM clients keep a single list on the server.

Well, apart from the expectations difference, there may be a technical surprise which is different from both traditional phone contacts and IM client behaviour:

Judging from the OP's report: "Delete all contacts" deletes contacts that have never been synced onto the phone. That's not even like an IM client, where you can at least see who you're about to delete.

Actually, there is a feature "Delete all contacts" that deletes them and does not touch IM lists. It's just a bit hidden under the "Contacts"-->"Settings" and I did not notice it at first.

My problem occurred when I manually deleted the contacts, by selecting them 10-30 at a time and using general contact deletion button.

Backups should be regular and accurate enough to trust on restore.

Are you seriously proposing to login every day to 10 different accounts on 5 different web sites, go through a list of 300 contacts, compare them with your word document or piece of paper, and update the ones that you've changed recently?

Or are you suggesting every time you add a contact, remember to write that change down somewhere else too? Possible, but a tad inconvenient and prone to forgetting from time to time.