is that possible?
if it is, how should i do that?

thanks.

No. MAC address does not propagate across a network.

you have to:
1) know your phone wifi MAC
2) get access to the wifi routers logs/DHCP lists
3) if you left ssh open - you could break in, reboot the device and find the gentleman who stole it by Nokia welcome theme

# man arp
# arp -a

How 'lost' is it? Is it simply mislaid in your house, mislaid in someone else's house, stolen or left in the pub and bought by Gizmodo?

If you know the MAC address of the access point then you can use this nifty thing to get pretty close to where it is

In the cases where arp works, the phone is probably already in your line of sight.

thanks for the information.

i do have wifi MAC, cuz it's printed on the box.
and i do left ssh open.
then now it's about how to do step 2 exactly?
would you please show me, thanks again.

What masloff outlined will only be useful (if you can call it that ) in very specific case:

This implies that you control that wifi router or have access to it. It also implies that your stolen N900 is using that wifi router - which obviously implies that it is in close proximity to the router - which leads to the conclusion you could probably SEE the N900 - or at least see it being used by somebody - and by see I mean visual eyeball contact

This implies that if you remotely reboot the N900 then when you hear the welcome theme being played you can catch the culprit who stole your phone - which implies that the N900 must be VERY close indeed for you to be able to hear it.

NOW, if you still want to know how to do it, wait for masloff's reply

I did something similar ages back when my dog chewed up my old HTC Magic and carried it off somewhere. I left wireless tethering on, so I just walked around with a laptop running kismet, reading the signal meters until I found it - stashed under my dining room table in a pile of crushed plastic and drool.