I think no one can answer these queries; however, maybe some can add information to build a bigger picture.
I have been running into issues with Openreach, BT, and Sky. Openreach arrives and says they cannot put fiber over the road or through the buildings and gardens at the back of my parents' home. The Sky technician arrives and asks where the fiber is because he cannot connect it. So, I am considering a data SIM-only router as an idea. However, it appears that an EE SIM-only router disables/blocks VoIP. By next year, in 2025, all copper phone lines are supposed to be turned off. If fiber cannot be connected to their home, they will have no phone service.
Another issue is that I live in a grade-listed building, so I cannot have a Sky dish or drill holes to pass fiber into the building. Presumably, where the copper cable enters the building, fiber could follow the same path. The mobile signal inside or outside is only 1 bar, while in the local park, it is 3 bars. However, despite the 3 bars in the local park, which is about a 5-minute walk from home, speeds have remained the same for the past 15 years.
We have four masts in the area. One mast is permanently switched off, according to Openreach; another has been vandalized by 5G conspiracy theorists (even though it is a 4G mast). Another has been turned down for no given reason. The one in town is not in line of sight and cannot penetrate the surrounding buildings. We would require more 5G masts, but there are issues with costs and access.
I can foresee some people, including myself, without a landline and in a place with only 1 bar, being unable to make or receive calls next year. In May, Morrisons' data team was here checking the area where the current copper cables run. I asked if this means we can have fiber in the grade-listed area. He said he thinks so. When I asked how it could be connected to the buildings, he acknowledged the issue, noting that his job only involves the cables under pavements. They pass a blue nylon cable from one end of the street to the next. If it fits and there are no snags, fiber will fit too.
Data router sim plan may not work for me.
I am basing the speeds around EE map and myself standing in same location and measuring speeds.
4.29 download not a usable speed.
makes it up data. 
