Our team was building a telco operator in the U.S. We already did that in several European markets and in Australia - so we assumed that we were mildly proficient in taxation issues. And then came the U.S. - a complete nightmare of overlapping rules that sometimes are not properly published. In essence you cannot do this on your own - you definitely need a tax service provider (like Avalara). Funny thing is though that you still are pretty safe to be noncompliant sometimes somewhere and the provider will not take on the liability if their data / computation was wrong. In short: a mind-blowing disaster. And you had to PRINT your tax forms and SNAIL-MAIL them to every jurisdiction that you were doing business in. I mean: hundreds or even more. Every. Single. Month. And don't get me started on the banking system stuck in Stone Age. I definitely would think twice to set up a business in the U.S.