If it shows on hook and you can receive calls, then you are registered. I suspect that what you are concerned about is the presence indicator. That requires additional ports to be open on your router, to function correctly.
http://www.3cx.com/forums/presence-indicator-connecting-38584.html
The fact that you cannot place a call, may be related to the outbound rules, or another option set against the particular extension. Try a call then have a look through the 3CX Server Log, there may be an entry that may help in identifying the issue.