Aloha,Most brands of handsets can be obtained as "storeroom" function, which are always locked and require a key from the outside.

We have been changing our exterior door keyed handsets and deadbolts to a better quality.

Please let me know if you would like a hand setting it up.

Flooring- for tile or laminate is also cheaper.For doors we bought at Home depot pre drilled for the handset but mounted the hinges ourself - $35 per vs $100+ for pre hung.Feel free to give me a call if you have any questions or I can help in any way.Thanks,BobPS Below are cabinets and granite we bought from BMO.  

After purchasing the handsets, I can change the cylinders in about a minute each.  

I would provide a minimum of one active jack (probably office or kitchen area) and the rest of the rooms can have a cordless extension handset, which don't require a separate jack.

If you're buying new doors, you can get them with no holes drilled for handsets.

I have work number and personal number both ring to handset.

We have done houses and a bare door (Nice 6 panel) drilled for the handset is @ $35 at home Depot, add $15 for a handle and labor to paint it and router the recess for the hinges.Paint the house - we pay less then $1 per sq foot for exterior

Consult a your CPA before hand, set up your entity, and you can likely write off a lot of these "discovery" expenses.