I use Pal on my iPhone, its ok. I wish that the administrator of the groups could control who joins the group before they gain access to the group chat. We use Palringo as an alternative method of messages from iMobsters by Storm 8. A number of times people have joined our group to spy on our conversations. By the time we figure out the situation several days have gone by.

Do they charge anything for it?

the app itself is free, but if you dont have a good data plan you might end up in trouble. You could always use it freely via WiFi