As your first solution with UAC module:
"As a plan B we instead opted for sending via uac module the invite to an
oversip instance (it's open-source since a week or two), which triggers
an HTTP request towards APNS, and on kamailio check with inv-timers
every few seconds whether the client came online in the meanwhile, then
complete the call. The drawback is that you can wait only for so many
loop interations due to the max branch limitation in kamailio (you'd
need to recompile it to set it higher)."
I read about the UAC module but feeling very hard to implement it as
your suggestion,
http://kamailio.org/docs/modules/3.3.x/modules_k/uac.html
Please give me and others more details about this?
Which functions those we need ?
Are they in: UAC module, Exec module, tm module ??
Thanks