Raconteur Media have published a special E-MONEY edition on the subject of electronic money and related subjects.
The following articles below are worth reading as they are about e-billing software, Euro industries, electronic invoicing and the role of the banks.
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“The hard road to electronic invoicing”
“The bigger prize”
“A challenge for the banks”
“The business imperative for legal-specific e-billing software”
Hele Hammer on 
Bruno Koch on 
I think the key here is the banks. Banks facilitating a way for small businesses to jump on board with electronic invoicing is going to make all the difference in the conversion.
It still seems silly to me though that there are still companies using snail mail for invoices. Just seems like a waist of time and money when the technology is there for a better world.