Honestly, any respectable SIP Provider would offer this sort of assistance directly and without charge.
the information in your SIP.conf file on an existing trunk can be duplicated with specific changes to host, username, secret, etc, changed based on the requirements of the SIP provider in question.
The support section of this forum is good for this type of help.
There are also several support forums just for Asterisk which will help. None of which will charge a fee, everyone is helpful.
I would be happy to help directly in real time, for a fee, but you really are better off with support forums.
Try:
http://forums.digium.com/ if you are really a beginner and need help getting an SIP trunk hooked up.
If you really want direct help, email me at
bill@poundteam.com. I will have to charge a small fee for real time help during business hours.
Seriously, try to do it and post your results. The community will help.