I strongly suggest a telephone call to the person who signed your acceptance letter. Only send an e-mail if you've already had e-mail exchanges with the admissions/scholarship folks. If you are truly telephone-adverse, a formal letter (as formal as your acceptance letter) is called for. Last year, I got an increase on a scholarship offer after telephoning the director and following it up with a nice letter memorializing what I expalined in the telephone call (with photocopies of comparable offers attached). They took two weeks to respond.
E-mails are great, fast, and convenient. But you won't stand out, and you'll especially linger in the in-box just as bold as the other 80 e-mails the director gets in a single day.