The setup above would be useful in scenarios such as the following: download emails in the morning, then work in the afternoon, and finally send all the replies in the evening.
In this case, downloading emails would be most cost-effectively done via PC’s Internet connection, since it’d be cheaper than using mobile phone’s GPRS connection.

The following are a few links with information to do that :
Psion to RAS
Psion to Internet via PC using MochaPPP
Psion to Internet via PC’s modem