I'd be happy to talk with you about whatever you're calling about

I've been getting several telemarketing calls per week at my home phone, and for a while I was worried about how I could reply to them: you know, graciously say no and try to hang up without being rude. But I've discovered a quick and painless approach that gets them to hang up almost immediately: reply in English. At the first break in their spiel, I kindly say something to the effect "I'm happy to talk with you in English about whatever you're calling about." And wouldn't you know it, they almost immediately apologize and head for the next caller on their list. (I figure if they do know English, I'll probably be so surprised as to end up giving / buying whatever they want!)

I wonder if this strategy could be used effectively in the US? When an obvious telemarketer calls, start the conversation in Spanish. If they are fluent, it's an excellent chance to practice!