Well, using Pidgin with OTR encryption you can have private (non anonymous)
conversations with them, if they use the same program. Problem is, it will
only encrypt text conversations, Pidgin has video conference chat available
for XMPP protocol, you can use it, but it's not encrypted. So, if someone is
spying on you, you will get your conversations recorded. I would therefore
advise against using gmail ;)
But, if encryption is not necessary, you can use Pidgin and OTR. It can even
be used in windows as a portable application, both of them, so, no need to
even install anything.
If using phones, you can try to use Ostel. Take a look at the guardian
project website. https://guardianproject.info/
Hope I helped somehow =)