In order to start a conversation with a text message, it has to be personal, so this is the best method available to start a conversation with someone from whom you have a cell phone number. They can reply to your first text message directly back to you and you can take on the conversation from there (i.e. for a big ticket, don't use a robot, your prospect is an individual, like you, that you want to respect.)
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.