Research by Plantronics in 2010 found that people who were experiencing issues in communicating by email and IM were able to solve the problem by a phone call. What’s really interesting is the different percentages – 71% for email, and 42% for IM.

My take on this is:
– With email, the rate is higher because the back-and-forth of conversation and clarification is slower. You don’t know when the other person will respond to your email message. Picking up the phone and calling them gets the issue resolved immediately.
– With IM, given its rapid back-and-forth nature by design, there is a lower need to pick up the phone. BUT – if IM drags on too long, such as because you or the other person is a slower typist – picking up the phone gets the issue resolved much faster. It amazes me watching people spending 30 minutes having a conversation by IM that could be had in 5 minutes by phone.

For more, see Richard Kenny’s presentation – Simply Smarter Office.