I think I know what te reason is. Now looking to get a solution.
The problem is that WebOS 2.2.4 needs a 'voicemailnumer' on the sim (I think it is the sim).
When you go to the phone-app -> preferences & accounts : there is a box where a voicemailnumber can be displayed. This is empty. There has to be a number in it, but I can't change it.
If I put my wife's sim in my phone, there is a number filled in in, and then there is no problem. An incomming call displays now the right name.
So, how can I put a voicemail number in the box there? (by phone-app -> preferences & accounts )