Imagine a gadget that fits in your back pocket and lets you surf the Web anywhere, write documents, make VoIP calls, watch movies, and listen to your entire music library. That´s not exactly what Nokia had in mind when it released the 770 ($360; nokia.com), a PDA-size Internet tablet with Wi-Fi and Bluetooth. But because the device has an open-source operating system, anyone can build new programs for it, endowing it with nearly endless functions (we´ve nicknamed it the HackBerry).