During that call you are providing your time, experience and expertise to answer questions and/or scope out work.That is time that’s requested by your client of you to be a part of a meeting that they feel is necessary. It could be about your project directly, it could be about a future project, or totally unrelated to anything that you are working on with them in the first place, but they want to pick your brain.As a freelancer you should look at  meetings just like you look at any other billable time. In fact, you should look at meetings as even more valuable because you are getting the opportunity to learn more about pains of your client, learn more about their business, and take notes on those things to become even more of an asset to them.