[dsfeez]

I lost my BB. who ever found it can he use it if he replaces the SIM card? Or can my carrier (Telus) make it obsolete with the serial number?

[NJBlackBerry]

Contact Telus immediately. They can bar it from their network. If someone unlocks it and puts in another carriers SIM card they can use it.

[Dubdub]

And if you are on BES, since you posted in the BES Admin section, tell your BES Admin immediately so they can try to wipe it.