How to hold an incoming call until the subscriber connects?

Question

Asterisk

There is an iPhone with the Bria program. She can work in the background and keep the connection to the server. But not satisfied with the battery consumption of 35% per day Bria sucks. The server has the latest ASTERISK + FreePBX
Task:
On an incoming call, make the following scheme:
1. Incoming call to the trunk
2. Pick up the phone
2. Run the command (in this case, I want to curl on the API of the sms.ru site to send an SMS to a mobile phone)
3. Response beep
4. Cycle of checking the asterisk ext subscriber for availability. If available, move on. If unavailable - do nothing
5. At the end of N seconds, transfer to voice mail or terminate the call
Points 1.2 yes, and 3.5 I know how to do. But how to make a cycle and a condition, I'm lost. A big request to help in the implementation. Thank you.

Answer 1

the usual queue is suitable
and you can put it in the parking lot

Answer 2

Rough version of solving a piece with a loop:

same => n(here),Dial(...)
same => n,Wait(5)
same => n,Goto(here)

Can be improved slightly by adding a limited number of iterations.
Also, the option proposed by Vladimir , with a queue of one member, will probably be more careful.