Useful Tool for Bulk Messaging

I use text marketer to reach a bulk of customers with the same message or a message which includes he same basic message but with specific details ie customer name, account details. All information is lifted from my database and is a relatively easy process. The reason I have given a 3 out of 5 is that I find about 20% of my sent texts fail to send but I still have to pay for them and I have no way of knowing why they didn't send.