every phone is different but I would check the owners manual first, a lot of phones will allow you to access a menu where you can change settings by dialing your phone number from that phone and then hitting star which will prompt you to enter a 4 digit access code and hitting #, then you will be given a series of setting options.......hope that helps, that's the way mine works

I know Verizon can set that,try calling sprint if they can't ask if that can be set in the voice mail options.