Cracked it !!!!
Finaly working.................................

Network settings

For Internet Access

Service = Orange Internet
Username = leave blank
Password = leave blank
APN = orangeinternet

For MMS Access

Service = Orange MMS
Username = leave blank
Password = leave blank
APN = orangemms

Msgs/MMS software settings

MMS Gateway Address = 192.168.224.10
MMSC URL = http://mms.orange.co.uk
alternate, both seem to work
MMSC URL = http://orange.multimedia
MMSC Port Number as = 9201

I use Gopherking's (http://www.gopherking.com) service for sending/recieving emails from multiple accounts (20 a year) and they assure me adding UK sites is high on their priority.

For Web access Blazer through GPRS for
BBC
ITN
Treo600essentials
TreoBits
Treo1
Gopherking

and of course a call to Orange MMS service (07973100451 (option 2)) to make sure data is enabled on account. It also appears to take a few days for it to activate which may have been my problem. (Expecting Orange to activate the account straight away (my impatience!)
Hope this helps others.
PS They don't seem to understand the term Treo 600 but mention Handspring and their little eyes light up !!!!

This is all using my 2 year old Orange SIM.

The phone is also unlocked and on version 2.09 FW. Inspite of Orange customer service being pretty poor IMHO they have the best network coverage and so, although the phone is unlocked I will stay with Orange. Technically the best maintained network for receiving all services on a 'pay as you go' basis, and presumably monthly tariffs have the same levels.

PS I use Panasonic SD cards. All the rest have caused me major problems when backingup and restoring software. I'm led to believe it's something to do with the voltage and speed characteristics of cheaper cards that make them less reliable. Have tried Sandisk, PNY and Lexar with little or no success. Panasonic, no problems (yet) and I keep testing it.