Problem about comucation between sip user and iax users

I know the comunication between two asterisk servers are used by IAX2 protocal.So the sip users can comunicate with IAX users. Is that so?
I have registered an account in I have registered my server to the voipjet,but i cant call the phone.Why?calling format is 186xxxxxxxxx Thanks

Never used Voipjet but do you have a register for your voipjet account? (this allow voipjet to know where you are) and do you have routing for your voipjet number? (so * knows which phone(s) to ring when you get a call)