The same way you can sweep Christians and Moslems into categories, WYSIWYG.
Do you believe in the one God of Abraham? Yes = all three.

Do you believe that Jesus was the Messiah (the offspring of that God on Earth sent to Save Us From Our Sins)? Yes = Christians, No = the other 2.

Do you believe that Mohammed was a true prophet in that the One God revealed His word directly to him? Yes = Moslem, No = the other 2.

Are you one of the original Chosen People (ie of Hebrew descent, especially - and sometimes only - maternally)? Yes = Jewish, No = the other 2. Note that this one isn't a question of belief but of ancestry, so in some minds you can't avoid it (like, the Nazis in WWII, and American Jews thereafter). Thus you can not believe in this God and still be Jewish. I, personally, would say "of Hebrew ancestry" in those cases, which would be closer to the truth as people understand the word Jewish. Not to mention that the Hebrews started calling themselves Jews when they decided to dedicate their existence to their God in the hopes of less future persecution, way back in the olden days. makes you wonder how that's working out for everybody...

So:
You can be Jewish by descent and believe that the Messiah has already come in the person of Jesus, which would make you both Christian and Jewish.
You can believe in both Jesus as Messiah and Mohammed as True Prophet, and be thus both Christian and Moslem. If you're Jewish by descent as well, I guess that would make you a Panabrahamite?

And I guess if you're not Jewish by descent but you believe in that God, but neither that Jesus was Christ {note the title, it's not a name} nor that God spoke to Mohammed, and then you would be Jewish.

Yes, these are gross generalities, but the terms Moslem, Christian and Jewish are gross generalities.