Hi Carsten,
Once SapPhone is installed the new SAP GUI 7.30 does not uninstall it. The transition from SAP GUI 7.20 to SAP GUI 7.30 does wipe out the telephony information and there are some methods to prevent this from happening. If you have a desktop image, make sure it includes sapphone or when a new PC's come in they can be reimaged.
Cheers,
Dan Mead