Both Call Manager and Call Manager Express will support 3rd party SIP phones. However you are going to have to manually provision each phone, you may not end up all phone features working, and there is not going to be any support from Cisco. Add the fact that this office is in Europe and you are not this is a recipe for disaster.
If you are stuck with a Cisco system, send the designer to
the Cisco page with the entire phone lineup. They might have something the designer likes better than the traditional green Cisco phone.
