If you complete this instructable you will be able to:
1. Make and receive calls over your cell phone using regular landline phone handsets (even with caller-id, sort of).
2. Access your voicemail using regular landline phone handsets.
3. Use up to three cell phones with the system at once.
4. Talk even if the power is out using a built-in UPS (optional).
This instructable does NOT require you to hack your phone (software or hardware), break the law, or do anything more technical than simple telephone wiring.
Step 1: You will need
2. An Xlink Bluetooth Cellular Gateway (this is the 'magic box', you need this).
3. Your home's existing telephone wiring, or supplies to do your own wiring.
4. A small UPS, if you want to be able to use the system if the power goes out (optional).
5. Some simple shelving supplies if you want to do a neat job and not have things tangled up in the closet.
6. Some basic tools, and an RJ45 or RJ11 jack to use as input.