Thanls Nicolas for your answer. Till now I've done exactly what you suggested for every ecommerce website built but I think that this is not the most elegant and also correct solution. Till now I used a radio field to ask if company is inside or outside EU, according to that I show/hide the VAT field but I should always display the VAT field, not hide, bcause if a user from outside EU want to prive the VAT number of it's company he doesn't have a field to type it in.
Would you please considere this as a feature in next releases?