1. please... DO NOT USE THE SIP FIRMWARE WITH THE 7970! It does not have all the features required for use of the 7970 as an orbiter.
2.the speed dial buttons can be customized, please see /etc/asterisk/sccp.conf, however due to some interesting bugs in the sccp channel for asterisk, using these buttons frequently will cause the entire sccp channel to die, rendering the phones dead until asterisk is restarted.
3. The background can be customized, but i can't remember off the top of my head the relevant page at cisco with the info... google it.
4. Hari and I are investigating writing a media plugin/player pair which will use the RTP Push functionality of the Cisco IP phones to push a stream of audio to the phone on demand, as well as record the output of the microphone back into the system. No promises on this one, this is research.