By now, you have a pretty clear idea of what you need to improve to reach your goal. But how are you going to do that? You need to form a hypothesis about what you think would work better than the message you have now. You may already have some ideas about things that might work based on previous experiences. Or you may have no idea where to start. You can start with evaluating some email/SMS marketing best practices and see whether these would fit for your business. You will only know whether these are suitable for you once you start testing, but it gives you a solid starting point. 
A custom sender ID, also known as an alphanumeric sender ID, enables users to set a business name as the sender ID for one way organisation-to-consumer messages. This is only supported in certain countries and are up to 11 characters long, and support uppercase and lowercase ASCII letters and digits 0-9.[12] Senders aren’t allowed to use digits only as this would mimic a shortcode or virtual number that they don’t have access to. Reputable bulk SMS providers will check customer sender IDs beforehand to make sure senders are not misusing or abusing them.
This question exists for many. First, NEVER EVER purchase a list of mobile numbers. (SMS/MMS) marketing is permission based, and ultimately you want a list of customers numbers who are genuinely interested in your product or service and are happy to receive your text message and are likely to buy your goods and service. Remember, you can turn customers off and possibly upset a lot of your potential customers when sending text messages on their mobile devices without their consent.