I work for a major telco as a customer service rep, and had this gem come through.
Cust: I've lost my sim card and need to have it blocked so nobody else can use it.
Me: Sure, what's the phone number attached to the sim
Cust: *quotes number*, I've looked every where for it.
Me: *pauses* That's definately the number?
Cust: Yes, I need it blocked.
Me: No need, your sim card's not lost...It's in your phone.
Cust: No it's lost, I need it blocked.
Me: Your calling me on the sim card now, it IS in your phone.
Cust: Oh... <hangs up>