i'm running the sip software with asterisk and don't have any problems. The newer ones don't register with asterisk but SIP70.8-0-2SR1S works great.
For the Orbiter be sure to put the right URLs in the "SEP<MAC>.cnf.xml" file (delete the link to SEPDefault7970.cnf.xml and put your desired config in /tftpboot):
It works perfect. The 7970 SIP image supports all xml push features (old 7960 and 40 with sip lack xml push because of limited ram, haven't checked the newer G series).
For upgrade instructions see the voip-info.org wiki.
I'll try to use the Aironet injectors (AIR-PWR-INJ) with the 7905 phones. Hope it won't fry. A friend has a 7970 running on a cisco poe switch (3800 series). The display is bright enough to be misused as a night light for the whole room. But as teedge77 wrote: you can't select full brightness from the menu.
There are newer single port injectors from the voice line with built in power supply. A good cisco dealer should be able to deliver them at about 50-60€. They support all cisco phones (old ones and new ones with 802.3af).