This is where the small chat systems become handy. Whether you will be talking with a client, a teammate or a friend, just a standards compliant browser & an internet connection will be enough.
Here are few easy to use & free disposable chat systems (text or video) for an instant communication:
Again a simple application where any number of users can connect. Optionally, you can password-protect your page to make sure the chat is private.
Besides standard chat rooms, you can signup & create private rooms which are password protected and the communication is encyrpted.