Using "All Calls" button for multiple lines on one phone

Question

I have several executive assistants that have multiple lines for executives that they answer calls for. We have added the "All Calls" button so they don't accidentally make outbound call using one of the executives lines. When the All Calls button is selected, all outbound calls are made using line 1. However, when a call comes in on one of the executives lines it doesn't show the name and number of the calling party unless you select the line.
How can we make it so the name and number show on the inbound call while having the "All Calls" button selected?

Answer 1

Little confused still by this, just want to make sure I'm clear.  My current set up with Asterisk is you make users which are extensions, and then enable voicemail on them, so for example:
Extension 300 - Voicemail enabled
Extension 301 - Voicemail enabled
Extension 302 - No Voicemail
Etc.  And it's there that you set the username/password for each extension.  So on a SIP phone, under Line 1 registration I'd have it register Extension 300, and line 2 could register Extension 301 and so on.  If someone calls extension 300, line 1 rings and if no answer goes to the voicemail box for 300.  If someone calls Extension 301, then line 2 on the phone rings and if no answer goes to voicemail for Line 2.
I do understand what you mean how each phone is it's own "User", and so the way I have it set up now is my 7970 is my user, and it has Extension 300 with voicemail assigned to Button 1 which works fine.
I just simply need a way so that Extension 301 shows up on Button 2 on the phone, so that I can select that line to make an outbound call (with a different caller ID), and if someone calls Extension 301, then that line on my phone with also ring, BUT will go to the voicemail box for 301.  I don't need my 7970 to light up that there's a vm or anything like that, it just needs to capture the vm.
If I make a floating extension or extension mobility for a new user with extension 301 and enable voicemail, then calling 301 does go to its voicemail box, but I'm just not sure how I would have that show up on my 7970 as line 2 and ring on there and make outbound calls on there as well.  Thank you so much!