we used to have ADB connectors for printers and keyboards, SCSI ports for external hard drives, floppy disk drives for something but all those have gone now.
Remember when ADB was replaced by USB? The only peripheral out there, other than the Apple keyboard, was an Epson printer.
Everything else was obsolete!
The new iPhone 5 connector will work with your Belkin with the aid of a small adapter.
Your G5 has had a good run and, in terms of computer years, is now past its prime and sliding the way of the G4 and G3 machines. Yes, they still run, but the world has moved on without them.
The wife's 3s can be swapped out for a very low fee, sometimes even $0.00, so there would be no problem there.
Just saying
P