Is it possible to get on GREX or a similar service using a Amiga 500, with a modem and the software Online!?
It is absolutely
not possible to get a GREX working on the amiga500 but it is perfectly possible to get an a500 online using a modem. These are two completely different things.
[edit] Or is it possible that you mean a "grex" other than the pci solution for ppc amigas?
