At my job I regularly receive calls and emails from people who want to make certain kinds of offers to sell my team some services, which don't interest me 95% of the time, although they could be interesting sometimes. Note that it's not part of my job responsibilities to take calls, or to accept or process these offers, it's something that I could do or not (I don't want to provide too many details about my job but let's say I manage a small group and have a large degree of autonomy).
I don't want to waste time talking on the phone to these people. I'm a busy person and I find that the phone is an extremely inefficient use of my time: if a call is unscheduled it interrupts whatever I'm doing, and even if it's scheduled, I have to allocate a slot for it, probably with some slack just in case it gets long, so it creates a large disruption in my calendar for something that in the overwhelming majority of the cases I could dismiss in 2 minutes if they just emailed me with their offers. Maybe in the 5% of the cases where I'm actually interested in the offer, a call might be worth it, but definitely not in the other 95%!
My problem is that, while when they phone me directly I just say that I don't take commercial calls and hang up, as I find totally rude to just phone and interrupt someone who you don't know (yes, clearly I'm not a phone person...); sometimes I get very polite emails asking me to arrange a time for a call. I don't want to do it for the reasons stated above, but I'm a nice person and it feels bad to respond to a polite email with a blunt denial.
I would be grateful for any tips on how to handle this kind of email requests so as to not have to waste time on the phone, while not coming across as a jerk, as I'm not good at this kind of diplomacy.