Bulk SMS to customers and particular area codes and prefixes - repost

We are located in Tulsa Oklahoma USA. We are prepaid wireless retailer and we would like to send bulk sms to our clients for our promotions. or all people in the same area code. we have done bulk Email to text messages in the past. clients will only belong to Boost mobile and virgin mobile wireless carrier . all other people with different network need not to receive the sms text.