In case someone thinks this stuff is simple and you can go with country codes for VAT: have you heard about countries like AX (Åland Islands, part of Finland)? Do you remember that GB used to be within the EU VAT zone, but now isn't? How about handling XI (Northern Ireland) and the migration of customers from GB to XI? Or (one of my favorites) — do you realize that parts of ES are not within the EU VAT zone (for example, Canary Islands)?
This stuff is crazy. B2B sales are relatively simple, but B2C is a nightmare.
Except when selling to your own country. But there, VAT is easy.
To expand a bit on the reverse charge procedure: It means the _buyer_ pays VAT. Which makes a lot of sense in B2B, since companies need to look into what local VAT they owe anyway. Adding the reverse charge invoices to that is easy. Not to mention that if they also sell goods or services, they'll end up paying little to no VAT anyway.
This stuff is crazy. B2B sales are relatively simple, but B2C is a nightmare.