How do I use the "second" line when my wife is on the first line?

[chevyman]

You can also use a two line phone. Harder to find nowadays but some companies still make them. I have a two line Siemens cordless phone that is probably ten years old now but still going strong.

if its a 2line phone you have to see if phone has 2 separate lines on the base unit and connect them to line 1 and line 2 on voip box. if it only has 1 jack then you need an adapter to change it to 2 jacks that are labeled line1 & line2 and plug them into your voip box line1 & line2.