E-mail is easy, and helps clarify requests and information, however talking directly with a Technical Support Engineer or Application Engineer allows an instantaneous flow of ideas. I’ve worked on a lot of customers projects through both e-mail and phone conversations and (without a doubt) the best way to work together is to combine the two media. Direct conversation should be followed-up by an e-mail to clarify the main topics discussed and to form a paper-trail should the same issue arise months or years later – or with a different set of people.