Here’s a DIY that is not only cost saving, but great in emergency situations. So your power goes out, and your phone is almost dead, take the time and have one of these phone line adapter charging cables made up and you’ll be all set! Most of the time phone lines remain in tact when there’s a power outage, (unless of course those are down from a fallen tree nearby)
As always check your local laws and policies before messing with someone else’s service (ie the phone company!)