Not everybody is offended (actually very rarely). Also a lot of your potential customers are probably doing their business mainly over a phone.
My assistant loves doing stuff like this, and paying her $MUCH_LOWER_THAN_MY_BILLABLE_RATE to save me time is a no brainer. (patio11 will be along shortly to encourage me to switch to weekly rates to avoid this scenario entirely, but yeah.) Calling up prospects to get their feedback on a product idea and chatting for 10 minutes, sending emails saying "hey, thanks for meeting with us today! We're especially excited about X and you can expect to from from us next week about Y", gently nudging clients about overdue invoices, etc. There's an upfront investment, but then you are able to focus on more higher-level stuff looking forward.
Oh and for the record, she has had instances where she had to track someone down via googley means because their cell changed, or business address changed, etc... and she was never reprimanded for "How did you get my number?!?!?" Usually they were grateful. Granted not always ;)