We call it free because you can use it as long as you want (if you not exceed conversation limit).
If you exceed you conv. limit account is blocked - yes. But this is because our protection. Every hosted account uses some amount of server resources and this amount depends on chats/conversations/page visitors count.
We can not afford uncontrolled conversations/chats rise on any free account...
However, you can always write to our support and ask us what happens and i'm sure we'll agree on something.
We do not want to lie to anybody. We just think that what we offer (even limited by number) is free and you can use it as long as you want.
(we have hundreds of customers like that)
But if you have some better specific suggestion, please share with us. We will consider it.