Yes. My understanding of GPRS is it simply uses idle voice channels for
packet communications. As the spare voice channels get filled up on a
busy cell, GPRS's through-put drops/dies.

PD

For those interested:

At the RF path, provided the BTS supports GPRS (as almost all do), the
signal strength will be the same. However at higher levels, GPRS Cell
reselection can be different to GSM Cell reselection. Cell reselection when
GPRS is supported is somewhat more complex, and depends on operator
parameters (particularly presence of PCCCH/PBCCH, MS Class, etc).  In the
case where PBCCH is used the operator is free to set different parameters
regarding weighting of cells, minimum required RSS, etc, etc. This is also
the case when the network sends PACKET_CELL_CHANGE_ORDER or
PACKET_MEASUREMENT_ORDER.

In the case of Australia, no operator uses PCCCH so the standard GSM 05.08
Clause 6 cell reselection procedures apply, when in idle more, except in
some of the states when GPRS attached when the network may order otherwise.
For those interested, support for the PCCCH can be activated in some Nokia
phones by entering the code *#pcc0#.

Now putting the technical stuff aside, it sounds more likely you have a
buggy firmware in your handset, which I would suggest having upgraded, free
under warranty.

Thanks to those who replied. I'll return to a Vodafone store when I get a
chance and see if they can either send it to get a new firmware flashed or
to get it repaired.

Can anybody advise who long it takes for Nokia to update the firmware?