I've heard of pom poms, is that the little ball on his tummy? What is it's purpose?

It is his scrotum and contains the testes if he has not been neutered.

Some vets neuter "pom on" by just removing the testes and leave the sac.

You may want to have your new glider checked by a Glider Experienced vet for a Well Check-up and since he probably has not been neutered - make arrangements to do so. The vet will be able to feel the pom and tell you if he has already been neutered by the pom-on method.

You may also want to check this thread for more information on male glider anatomy:

http://www.sugarglider.com/glidergossip/topic.asp?TOPIC_ID=2849

Neutering will help reduce your glider's marking of the cage and will keep him from developing a very strong odor as he matures.

It will also allow you to get a female cage mate for him if he does not have a buddy. It allow your gliders to be wonderful pets with out the worries of dealing with joeys.