Getting old # back

My father (account holder) recently passed away.  He had digital phone service & internet.  I moved up to take care of my mom.  I needed to get a different internet provider for higher speeds.  I cancelled the internet and home phone because I was told they were tied together.  My mom wants her phone service back but no internet.  The home service is disconnected but I want to see if it is possible to get her old number back or when the old number is called, callers will be made aware of the new number if I decide to get new service.  Is this possible? Thanks in advance for any information you can provide.