Well, I use a couple of different telescopes... I use the Oggs 'n Ends-- okay, technically the Oggs 'n Rose telescope from Parsimonious. There was a white one from a set called White Witchery, which matched, but that one seems to be down for the moment (they're probably updating it; they keep doing that lately). There's also one in the Alchemist set from The Dark Project, and Lord Darcy Updated the Sims Design Avenue Alchemy Set telescope for Free Time. (If you don't have Free Time, you can find that set here. It's a very pretty telescope.) They're not replacements, but buyable telescopes cloned from the expensive telescope-- they'll get you your alien abductions!

I do not do mesh replacements, I'm afraid-- I haven't tried meshing and even using somebody else's mesh as a default is beyond me just now. I'm sure it's possible to change the UFO to something else, but it would have to be something else that flew, given the animations for when they're abducted and returned... and I don't know if you could change the way the UFO looks in the cinematics at all.