I had a customer ask me why they couldn't see their multiple lines like how they used to with their old PBX, after explaining the numbers are now just directed to groups of phones and they dont need to see the lines themselves, i started to think if there was a way to show individual lines.
I would say no, not really. This is partially because they way voip systems like RC are designed, but it was the same discussion years ago when people went from their old square key systems to more advanced PBX systems too.
There are only so many buttons on a phone and only smaller businesses have so few lines they could all appear on all phones. Affordable 32 button key system and PBX phones used to be fairly common, but voip phones with that many buttons are rare if they exist at all.
That said, the best way I have found to replicate the square key experience for customers that need/demand it is to use park location buttons. This allows for small businesses like retail shops to have a few buttons that are the same on every phone and can be labeled line 1-3. When they have a call in progress they can just press an available line to put the call on hold and shout "call on line 2" and anyone can pick it up form any phone.