A note on the use of technology from a former real estate agent..... it may be that he is not comfortable with the tech. I was astounded at how many of my real estate colleagues did not understand how to use e-mail, would refuse to check e-mail, and one actually asked me why her laptop stopped working (she didn't plug it in to recharge the battery - she believed that the battery was a self-contained powerhouse that never stopped powering the computer).
Or his communication style is different than yours. Some people are phone people. Some people are e-mail people. I hate the phone, and I prefer e-mails because I have documentation of the conversation - but there are people I work with that I have to call because they are phone people and if I wait for a response, i'll be waiting for a long time. It sounds like John is phone people.
Call him. And see if that works better for you.