(Picture of undeveloped fruit...)

I've never seen plums with those long stems. I'd be concerned it might be an ornamental plum if it's even a plum. Looks more like a crabapple???

Well that would sure be a disappointment. Is there anyway to tell the difference or how many years will I have to wait to figure out what kind of tree this really is?

I really had no desire to have a crabapple tree and don't know much about them besides their flowers and fragrance are nice. Are the fruit edible? Thinking it could pollinate an apple tree though....

A plum has a single seed inside. A crab apple has several seeds in compartments just like a regular apple. Cut one of those fruit in half and you can easily tell if it's an apple or possibly a plum.

I do believe it is a crab. Yes it will pollinate an apple tree.

That appears to be a crabapple tree. The stems on the fruits are long. The bark is smooth. The size of the fruits is too small to be a named variety of plum at this point in the summer. The crabapples will be edible but may or may not be palatable. Yes it will do a good job of pollinating another apple tree. Or you could graft whatever apple you want onto it.

Cut one of the fruits open and there are (4) seed chambers. I guess my plum tree has become a crabapple tree.