Climb up the career ladder so you can obtain the Resurrect-O-Mitron in the career reward screen. The second method is after your sim graduates from university, find a job in the paranormal career.
How do you get the Grim Reaper phone on Sims 2? That’s how it works for Sims, I guess it is the same for pets. Beware though, because if you don’t pay him enough money he’ll bring your beloved Sim back as a zombie (ew I hate zombies). You have to pick the person you want and you have to pay the Grim Reaper a sum of money to resurrect the Sim.
