Just a note for those trying to use PCMCIA NIC's. The standard 3Com 3C589C or 3C589D works with the Enterprise version of 5.0.5 by simply installing the driver supplied by SCO. You do have to configure it properly: slot 1, address 300, IRQ 3, shared d4000 - d6fff, media/cable as auto. There is no need to pay high prices for third party software, unless of course you can't find a 3Com card. This is not a slight on Lynnsoft's drivers, believe me, I have used them and they work great with terrific support, but, if you don't have the money to throw away, the 3Com is worth a try.
Be VERY SPECIFIC on the card. When I say 3C589C, I MEAN 3C589C - NOT 3C589.
Now, as for the modem, well I have not had need to use one, so my guess is Lynnsoft would be a very good solution.