oxnsox: If you look under Extras and Info
for your phone you will find:
Manufacturers name: an RM number,
this is the model and sub model.
Mobile Operator: this associates with the carrier firmware variations, and likely dictates who determines your firmware update
Check your devices and see if three Mobile Operator is the same on both devices.
The 640 mobile operator is Vodafone.
The 640XL mobile operator is 000-NZ