actually i used ziphone (ziphone.org) for my iphone (non-3G) and i have installed a plethora or free 3rd party apps including agile messenger, fring, a video recorder, devicescape, summerboard, and a whole bunch of other stuff. as far as i know the old iphone has owned by the independent dev teams and thus resulting in a mess load of free apps far better than anything the apple apps store could ever offer.
once i unlocked and jailbroke my phone using ziphone it automatically replaced the installers pre-loaded apple apps store with a list of 10+ 3rd party sources for free apps. Some are free to try for 30days or so but I understand that cuz some of those dev teams make a living off of this on their own instead of apple.
As far as I know about the 3G iphone, only 1 dev team (somewhere in brasil) successfully unlocked and jailbroke the new 3G model. More will come in the next few months. And I guarantee by january there will be no-holds-bar on the 3G in terms of unlocking/jailbreaking and free 3rd party apps just like the 1st gen iphone.