The answer to the one part is -Yes- you can connect to your sip/iax to app_rpt extension on the system.
Nothing extra is needed but the sip definition in the system and a compatible sip phone/software on your network.
Not to be taken the wrong way,
I would think many of us could help you through that but,
We have no way of knowing how much you know about the supporting structure, being asterisk pbx.
So I would say that you should look-up the support you need from asterisk online manuals on setting up a phone sip extension. Get the manual for asterisk at
asterisk.org and you might learn about the many capabilities of asterisk why you are at it.
When you have a particular problem doing that, ask that particular question. Many are glad to help.
Here is my sip extention for my ipad (with sip software)
--sip.conf
[6010] ;iPad
deny=0.0.0.0/0.0.0.0
username=6010
secret=yoursecretpassword
dtmfmode=rfc2833
canreinvite=no
context=radio-control
host=dynamic
trustrpid=yes
sendrpid=no
type=friend
nat=no
port=5060
qualify=yes
qualifyfreq=60
transport=udp
encryption=no
callgroup=
pickupgroup=
dial=SIP/6010
That should get you started but get the asterisk manual. Many answers are in there.
...mike/kb8jnm