Consider the following image.
The default basic CTI offering in Sage CRM v7.1 used the frameset structure as highlighted in the above image. Sage CRM has a very flexible set of APIs and there have always been several hooks in existence to allow other companies to create CTI software that can be integrated. There are also partners who have created other extensions to extend the capabilities of the system.
The CTI button frame and a frame for the CTI object no longer exist in the same way in Sage CRM 7.2. The removal of the frameset will have an effect on the way any customization that depends on CTI interact with the screens. If you are using a 3rd party CTI integration you will need to seek your suppliers advice on whether this has been updated for Sage CRM 7.2 before upgrading from an earlier install of Sage CRM.