A:AnswerYes this phone will work on a different floor from the base unit. We have the base unit downstairs in the kitchen and two of the extension handsets upstairs in bedrooms and they work just fine.
A:AnswerAccording to AT&T website, the CL82465 is compatible with the CL80115 handset extension. AT$T sells them for $19.95, plus tax and shipping. Amazon sells for $19.99 with free prime shipping.