This may also get compounded by the fact that they are starting to wind down 3G mobile signals.  I am lead to understand that some SMART meters use 2.5G but there are some out there using 3G sims cards.  Question is will the meter need to be replaced or just the sim card, either way this will use up resources. 

Question is will the meter need to be replaced or just the sim card,

Given the life of a mobile comms standard is a lot shorter than that of a traditional  electricity meter there will be some changes...

Certainly those meters that had a design freeze before the 4g stuff was standardized will have to be changed or internally modified.The saving grace, perhaps, is that most designs I have seen use a 3rd party radio board configured to act as a usb  'comm'  port connected to behave like a traditional serial modem, rather that soldering  the RF chips on board.

This is either in a box of its own, or plugs in as a daughter card to a socket on the main PCB which provides it with power and a few data lines-  The sort of folk who design the electronics for electricity meters are not up for designing what is in effect about half a mobile phone - the NRE cost is too high and cannot compete with the folk who make phones already and simply take a current design and remove the keyboard, speaker microphone and display parts.

I imagine that if the market is large enough for any given model of meter then a suitable 4g or 5g capable module will be made that is form-fit-function replacement for the previous 2G/3G one and the main meter PCB and case design can remain unaltered. There is likely to be an antenna change for different frequencies though.

And that means that some places that were in coverage on the old system will no longer be and maybe vice versa

Then in parts of the UK where things are a bit thinnner they do not use the mobile phone networks at all but a a dedicated service from telfonica

it is however a bit of a mess.
Mike

I think most of the SMETS 2 meters have a separate pluggable "communications hub" on the top of the meter (to cope with the soft southerners who have to use the mobile phone network, while the rest of the UK has a dedicated long range radio system) - so even if the mobile network has to change it should be a simple snip seals, unplug, plug and seal operation.

www.smartme.co.uk/smets-2.html

   - Andy.

I think most of the SMETS 2 meters have a separate pluggable "communications hub" on the top of the meter (to cope with the soft southerners who have to use the mobile phone network, while the rest of the UK has a dedicated long range radio system) - so even if the mobile network has to change it should be a simple snip seals, unplug, plug and seal operation.

www.smartme.co.uk/smets-2.html

   - Andy.

Will 4G or 5G signal work under my stairs?  Only time will tell.