Cisco 7960 SIP can't dial when calls come in

Okay, so I know that these are old phones and there probably isn’t anything that will help, but I figured I see if anyone can answer this.
I pick up the receiver (I can’t get on-hook dialing working), and start to dial a number. If a call starts ringing to the extension while I’m in mid-dial, then I can no longer see the number I’m dialing, nor finish dialing it if someone else picks up the call. It wouldn’t be a huge deal, except there is no “ignore” softkey, and I can’t figure out how to add one. Any ideas? The boss doesn’t want “ignore busy agents,” but that’s the only reasonable thought that I’ve come up with.

Yes you are totally correct, it is up to the phone as to whether it will override a call in-progress and take an incoming call in preference, there is nothing that FreePBX can do about that, if there is an option in the phone’s provisioning, use it, if not well . . .