Leave voicemails asking people to reply by email instead of calling back. Send them around 11 am or 4 pm when inboxes are quieter and your message is more likely to get noticed.
When you think about the call patterns that you use, your voicemails— I use the voicemail to encourage an email reply. I don't ask someone to call me back. As a matter of fact, I say, you don't need to call me back, but if you could reply to the email I sent, I would greatly appreciate it. All right, time of day that you send can be a differentiating factor. I like 11 and 4 because most people don't book meetings at 11. They don't want to interrupt lunch. Most people don't book meetings at 4. They don't want to interrupt going home. Make sense? So that's my diff— some of my differentiating factors.
