O2 Atom Exec + Three SIM = Unknown sim status...help!

[jpd1009]

Hi,
I have an O2 Atom Exec, bought off the shelf and 'unlocked.
Been using it for ages with Optus.
Changed to Three (austalia) and now I get the 'Unknown SIM Status' message appearing.
The SIM works OK in the handset I got with my plan, but really want to use the Windows Mobile device.
Three customer care have given me the spin ... "its not going to work", however I am not convinced.
Any help with this would be greatly appreciated.
Thanks

[bchchang]

O2 Atom Exec = GSM network only
Optus = UMTS 3G & GSM network
Three = UMTS 3G network only

understand now?

[hendranata]

exec can umts...

[nikvan8]

So if I have O2 Atom I can't get on the 3 network in Australia?

[Duwenbasden]

The Atom Exec isn't 3G / UMTS compatible. GSM only.