Maybe this can be achieved via settings I am not aware of. If not I will submit a feature request.
When a call is coming in while I am in the process of dialing it should be handled via the call waiting user interface. That’s how Digium phones do it. Your partially dialed number is assigned to one “line” while all other incoming calls are presented underneath (on separate “lines”). Using the arrows allows one to go back and forth. So one can take a call or actively reject it then return to the partially dialed number.
Right now the S500 phones simply ignore the call if you “opened the line” (you do that by either picking up the handset or pressing the soft button assigned to the line - this state is denoted by the button being lit green).
If you have not “opened the line” (you just started dialing) the S500 will overwrite what you were doing (you lose what you dialed and have to start anew) and present you with the call.
At the very least is there anyway an S500 can be set so that the act of dialing automatically “opens the line” (lits green the soft button assigned to the line)?
Edit: I am using FreePBX and provisioning with End Point Manager.