Before cell phones, I used to carry a nationwide pager. My pager went off just as my flight out of IAH started to board. Something had gone wrong at a recently-installed client site and I was the most knowledgeable on the particular issue.

Problem was, I was on my way to EWR to attend a different client's implementation meeting, so staying in Houston to work the issue on a landline phone was not an option. Boss said to call client on the Airphone - it took two hours, but the issue was resolved and the client was very happy.