Theoretically you can summon any one and any thing. It gets much harder over great distances, and once you are summoning a sentient being it can get iffy because of their will. For example if we were next to each other and I wanted to draw you closer, assuming we were friendly, it would be much easier than if you were resisting the spell. Or say a hundred kilometers away. Actually, at that distance. Simple summoning spell would likely not work at all. You would probably need considerably darker magic at that point for people. Items, I do not think would work at all. However I have never tried.