Stop outgoing calls

I want to use the mobile retro style phone for my mother in a care home but don’t want her to be able to make outgoing calls. Is there any product for this or is it possible to remove the keys?

There are two possible solutions:
1) open the phone (4 screws at the bottom plate) and unplug the rotary dial/key pad cable
2) the OPIS mobile phones come with some undocumented features such as: allow only short dials, block certain numbers, auto dial when the receiver handle is picked up.

As far as the latter is concerned, please have a look at the attached document. If you use MOD3 but do not actually assign a number to short dial *1 you should have the desired result.