CF'ing is a typically a telephone company provided feature. It usually has nothing to do with the type of phone you have. In your case the Starplus STS is not a regular phone. You have a digital key system. I believe the Starplus system does have the capability to fwd call's internally, but typically it's still done via the telephone company. If the feature IS on there, it would mostly likely be on your main line. You would dial *72, listen for the dial tone to come back, then dial the # you wish to fwd the calls to. You might have to let the call complete before you hang up in order for the call forwarding to take affect. Your best bet is to call you local phone provider and ask them for directions on how to use their call FWD feature.
10+ years telecom experience.