When I hear or read "Эй" referred to me the first thought I have I do something wrong. In English it seems to be ok to draw somebody's attention with "Hey" or "Oi". In Russian I feel negativity coming from this exclamation.

It's better to write "Привет, любимая. Я получил твою SMS и она мне понравилась. Что у тебя нового?". "SMS" has feminine gender in Russian ("СМСка") regardless of that thing it is "message" (сообщение).