Yes but that general type of call forwarding only works between two active line phones (and not sure if bidirectional). Continuity call forwarding is different since it works with an iPhone and a second Apple device that is not an iPhone (Mac, etc), no second line required. So it's a different function.Call forwarding has been around longer than cell service, if you are worried about missing a call when away you could always forward your call to another number.. same concept on the iPhone and backup/burner scenario.. I purchased a prepaid yearly plan for $240 and when I go out to a crowded/sketchy area I forward my iPhone number (and wife’s) to the backup which contains no personal information or apps.
It's unfortunate Continuity call/SMS forwarding doesn't work with a second iPhone because it might be beneficial to someone who has a spare inactive iPhone they'd like to use as an "iPod touch". The reason I found out it doesn't work between two iPhones is because I wanted to use a small iPhone as my main iPhone when I was out and about, and when I came home I wanted to plug it into a charger and leave it and use a bigger iPhone at home. But not being able to send and receive calls and SMS messages prevented this for me.