Definitely understandable. To me, "Oh Hai" comes across as unprofessional, not laid back (which is what I assume you're going for.) The "Hi; I'm Tim." seems to

Definitely understandable. To me, "Oh Hai" comes across as unprofessional, not laid back (which is what I assume you're going for.) The "Hi; I'm Tim." seems to work a lot better in that regard.