Right next to Potsdamer Platz in Berlin you will find the Sony Center; a collection of restaurants, shops, museums and even a movie theatre. And, of course, a Sony Style store. In terms of Wi-Fi, there is a T-Mobile/T-Com hotspot in the Alex cafe (right next door to the Sony Style store), and there is a free hotspot in the Sony Store itself (network name Hotspot_SonyCenter).
Both of these are now supported by Devicescape so you should be able to get online either while browsing the latest Sony gadgets, or while sipping a coffee at an outdoor seat in the forum.