T28P on Asterisk (freePBX) only 1 line accepting calls

[arhi]

> Have you tried to first setup 1 ext only per phone and call the ring group?

I want to use 1 ext per phone. Do you mean 1 ext per line? I tried that it works but it's not what I want.

> It would be good that you use a SLA featue that can share your line.

Not sure I understand. Isn't this SLA thing so that same extension can be on multiple devices and then they can all join in single call?

The manual for 28P show that I can have lines with same and different subscriptions, the other phones I tried do this out of the box (looking at 28p manual so should it too). Not sure what am I doing wrong