OK, ill give you the 30 cent tour.
It is a requirement for all passenger lifts to have two way communication to a manned station.
For practical purposes this usualy means an autodial unit connected to a BT line.
The line is provided by the tenant /client.
The OEM lift companies (OTIS, schindler and TK) develp their own in house control systems and because of the requirements of EN81-28 at the same time "bolt on" at their factories on the continent their own propriety autodial units.
Because in the main on the continent companies in the main stick to their own kit.
In the UK the market is more flexible and people like me who own independant lift companies "mix it up a bit"
OK so far, if the lift is under maintenance at this time with the OEM, schindler in this case then there is no problem.
However if you have changed service providers (even to people like me)then the autodial unit if it is an in house OEM unit cannot be re programmed to anyone other than them.
So TK by highlighting the issue are doing you a favour.
Imagine anyone being in the lift and it has no means to folk to summon assistance!
Also the fact the lift is not being used often is no excuse as the safety systems, including maintenance and communication systems must always be in place as should you bi annual LOLER or competant persons inspection by an authorised body other than your maintenance company.
If these systems are not in place and an incident occurs then the directors of the management company will be liable for investigation and possible prosecution by HSE.
So if you have swapped providers then you have no option than to fit a new autodial unit.
However you need to ensure for your sake and future re programming if your provider of lift services changes in the future that the system fitted is generic, ie: a Memco or Windcrest type system.
Does this help