I get cold-called at my girl's house every so often
The conversation usually runs something like this:
(imagine that the cold caller has an impenetrably thick Indian accent)

"Hello, I have information here that your computer is running slowly."
"I'm sorry?"
"I have information that your computer is running slowly, would you like me to fix this problem?"
"What problem?"
"Your computer is running slowly, but we have the solution."
"How do you know my computer's running slowly?"
"We got this information from your ISP."
"How do they know?"
"How do they know what?"
"How do they know that my computer is running slowly?"
"They passed the information on to us."
"So...who are they?"
"Who are who?"
"Who's my ISP?"
"ISPs are companies like Virgin, Aol, Bulldog broadband that supply you internet."
"Yes, I know that. You said my ISP passed information onto you about my computer."
"Yes, they said it was running slowly."
"So who is my ISP? If they are passing you information, you must know who they are."
"We have that information, yes."
"So...who are they?"
"Who are who?"
"My ISP."
"We don't have that information."
"Wait, you're telling me that my ISP sent you information about my computer without identifying themselves to you?"
"We don't have any information about who your ISP is, no."
"So someone, potentially my ISP, potentially someone pretending to be them - or not, since you don't even know which company this information is coming from, told you that my computer was running slowly."
"Yes sir."
"And your solution is...?"
"We have special software that will speed up Windows."
"Windows?"
"Yes sir, Windows is running slowly on your computer."
"Is this the information you got from my ISP?"
"Yes sir."
"Which you can't tell me the name of."
"Yes sir."
"I think there's going to be a bit of a problem here, you see I'm a network engineer, and all the computers in this house run perfectly fine. Windows isn't slowing down at all because my server runs Linux Apache, my laptop has Ubuntu and the Mac...is a Mac."
"So your computer isn't running slowly then?"
"Wait, let me get this straight, someone claiming to be my ISP told you that I had a computer running Windows that's too slow?"
"That is the information I have here yes."
"Yet I don't have a computer running Windows in the house."
"No sir."
"So someone has been feeding you misinformation about me, wouldn't you agree?"
"Yes sir."
"Could I speak to your manager, please?"

*repeat conversation from top of post until they get so exasperated with me they hang up*
( emvee cruor deo cruoris, Thu 3 Sep 2009, 14:38, 5 replies)

Haha, I'm completely unsurprised
I work in web usability\accessibility, and got a phone call from an Indian firm.
Them: Hello Sir, did you know that your website has several accessibility issues"
Me: "Really, well now. Perhaps you could explain them in depth to me"
Them: "Yes sir, they are probably with the accessibility of your site"
Me: "We've established that, but my job, as you would know had you looked at the site, is assessing the accessibility of other peoples websites. You'd think that my own site would be somewhat accessible."
Them: "Erm, ah, er"
Me "Bye then"

Tossers
( LemonEntryMyDearWatson This time, Moriarty, the hand is on the other foot, Thu 3 Sep 2009, 14:42, closed)

Clearly...
...they're trying to sell you a ramp for disabled visitors.
( Scaryduck LIKES EGG, Thu 3 Sep 2009, 14:47, closed)

Sadly, they probably were
Even sadder, some folks have probably ended up buying a disabled ramp 'for their website'.

Possibly
( LemonEntryMyDearWatson This time, Moriarty, the hand is on the other foot, Thu 3 Sep 2009, 15:34, closed)

Whiskey Tango Foxtrot?
Never heard of this scam, but cheers for the info - 'tis always amusing to hear of the depths low-life scum will sink to.
(_(_(_(_(_(_(_(_(_ =o.o=, Thu 3 Sep 2009, 20:10, closed)

Sounds like you got
fonejacked... www.youtube.com/watch?v=M8woC9B30zE

Or the real-life equivalent, anyway.
( chart cat has an itch, Mon 7 Sep 2009, 5:22, closed)