You must choose a proxy (or set up two trunks - one for each proxy) - so use cust02.sip.weblink.se or cust01.sip.weblink.se as host.
Create a SIP Peer:
username = <username>
type = friend
secret = <password>
insecure = port, invite
host = cust02.sip.weblink.se
context = from-pstn
canreinvite = no
qualify = yes
and the registration:
<username>: <password> @ cust02.sip.weblink.se