I use GoToMeeting and am very happy with it. Even for a small business, it is worth the cost. If you use a free thing like Facetime or Hangouts, your clients will need to register and set up, etc. I like being able to launch a call or video conference NOW, send you a link, and BAM, you're in.
If you require a PIN, GTM will ID your callers. I've never experienced unidentifiable callers. What's your application?
Hey, Sheri! You can use solutions such as Zoom, or messaging softwares that have calling integrated within them, such as Skype and Slack, to name a few. As Chris mentioned below, GoToMeeting is a great solution, as well, as is Google Hangouts for basic and cost-efficient needs!