I'm trying to help my parents.  They had ADSL broadband, but due to their rural location, they could only get a maximum of 1.4 Mbps download, and frequently experienced periods where they had complete losses of service for hours at a time.  After contact Spark technical support (who were pretty hopeless, incidentally), I elected to move them to Rural Broadband.  I decided to keep them with Spark, on the expectation that the plan they would go on would retain their landline.

What I did NOT realize is that Spark apparently have a different interpretation than I of "landline".  I figured that this meant that they would retain their copper line to their house, and have their phone services through that.  They would be given a cellular modem to plug their internet into.  Not so.  Spark disconnected the copper line, and expect them to plug their phone into the cellular modem as well.

So:  Here's my issue:  My parents have (had) four handsets in their home, including one in my father's workshop (~80 m from the house).  They can only plug a single handset into the modem, so now only have one handset, which they are pretty frustrated about.  So I am looking at options to restore their handsets in the various rooms.

Can anyone please suggest good options for this, and help evaluate the ones below?

1.) I guess I could just ask Spark to reinstate the copper phone line back to the house.  I expect that would be expensive, and a pretty high monthly cost.

2.) Spark suggested getting a base station with wireless handsets, such as a Uniden XDECT 8155, which allows up to 12 (apparently) handsets from the one base-station.  Not sure if the wireless range would be sufficient for the 80m out to the workshop.  But that will cost them about $400 (apparently its $200 for the base station, and $100 for each additional handset - seems a rip-off)

What else?

Is there some kind of adapter that can effectively convert the telephone signal from the modem, and feed it back into the existing telephone wiring in the house?  That would be an elegant solution.  I can't just get a signal splitter and do that, can I?

Any suggestions gratefully received!