It would be really great if when you save a number you can say whose number it is. Currently you can just say main/personal.
In the extension field you can't write their name as it wants a number.
Many clients just use mobiles and there may be a few different people at a client - we need to be able to add several mobile numbers to a client and say whose numbers they are.
I'm looking at this slightly differently - as we often do at Onkho!
Perspective #1 : Contacts and relationships
Today what we have is a sea of contacts that you can create relationships with so in your example, 3 contacts for a client is 4 contacts in Onkho. So what I would like to see is that when you look at a contact, you also see the contact details for any of the related contacts.
Perspective #2 : Types of contact details
Today we give you standard out of the box labels for emails, addresses etc. e.g. home, main etc. I think you should have the option of providing your own label. This is how mobile address books work now (finally!).
Both of the above would solve your issue in a more elegant way and give you much more flexibility. For example it would be very easy to turn the Director of a Limited Company client into a client by simply adding a Tax Return service to them :)
Hope the above makes sense despite the copious repetition of the word "contact"!