Thanks Demeter - you may be onto something. Digging a bit deeper:

 

 

 

 

2G Network

 

GSM 850 / 900 / 1800 / 1900

 

 

 

3G Network

 

UMTS 850 / 1900 / 2100

 

 

 

 

 

UMTS 900 / 2100 / 1900

 

 

 

 

Might need to force UMTS, rather than the current Dual Mode.  Will try it out next time I get my hands on a C2