Collisions between a particle and the corresponding antiparticle are just like any other reaction -- it takes place provided there is sufficient energy, and provided that no conservation law is violated. It's not true that "all" of their rest mass gets released as energy. Part of if goes into creation of other particles, and part of it goes into supplying these new particles with kinetic energy.
For more than 25 years the Tevatron at Fermilab collided protons and antiprotons. Here's a picture of a typical collision showing the shower of particles it produced.
When a particle reacts with its own anti-particle, all the conserved quantities (electric charge is just one of them) cancel out so it is possible (but not required) that all the particles energy gets transfered to a number of photons. These photons will be absorbed by the surrounding matter heating it up.