Is there a way to dial feature 71 (CO Link) on a single line set?

The Link feature from the S.line phone is *71,thats will generate a link signal to access the features from your Teleco.

Good Luck.

Do you mean from an ATA ??

It would be LINK *71

Any feature from an ATA is done by doing LINK * and then whatever you would usually press after pressing FEATURE.

Meridian Man