Upgrade CRM 4.0 to 7.0 - SAP-GUI vs WEB-UI

We will start in a few month a project to upgrade our CRM 4.0 to 7.0.

Today we use SAP standard for business partners, transactions like activities, middleware, IPC and a lot of customer development with huge business logic.

1. Do we have to migrate our whole SAP-GUI developement to WEB-UI ?

2. I have heard that some SAP-GUIs (i.e. business partner) are not longer supported, only in WEB-UI ?

André