Make multiple calls in Gmail

According to the official Gmail Blog, their new multi-call capability allows you to put callers on hold with Gmail's phone service, picking up another call at the same time. This is not a conference call feature but rather, it is more like a call-waiting feature.

If you’re in a call and make a second one, your first call will be put on hold while you talk on your new call. You can switch between calls by pressing the “Resume” button on the call you want to talk on, which will automatically put the previous call on hold.

Gmail Multiple Calls

» Make multiple calls in Gmail | Official Gmail Blog