This is where I've found email to be remarkably helpful. Of course you may not get the kind of spontaneous expression you get by phone or in person. You may need visual or auditory information that email can't provide. But with email, you do often get considered, detailed answers to your questions, which you can refer back to later without having to take notes yourself. You also--and this is key--have the opportunity to ask further questions in a relatively unobtrusive way, and the interviewee has the same chance to send more info when he thinks of it later, which he often will. You have specific examples in the interviewee's own words of professional or personal language--with no chance you misheard or mis-transcribed it. And you--or I--feel less guilty because you've allowed the interviewee more control over when and where he answers your questions.
In short, for my fellow introverts, asking questions by email is way better than not asking them at all ... and can bring you truly surprising and useful results.
This has been another edition of Stuff Other People Have Known for a Long Time But Is Exciting News to Me.
For when the phone is just too much.