How can people change your voice greeting when they don't have access to your phone?

this mystery greeting bumps off my regular greeting and goes something like this: ';The FCC has determined this number is operated by a vulgar person, proceed with caution. Number 3209';How can people change your voice greeting when they don't have access to your phone?
lol... looks like someone is pulling a prank on you... to change a greeting from another phone wll you need is to call that phone and press # ... that goes to your voice mail... that person must have you password to enter and then he/she can change the greeting... pretty funny prank though