What's a free way to send out a general text to 15,000 phone numbers I have?

I have a list of names and phone numbers with their consent to mass text them. But I still don’t know how to do it. I’m terrible with cell phones. Can I use the AIM service for such a thing? Should I buy a dedicated cell phone? What do I do… to accomplish this without having to pay a vendor 10 cents or more per name? I want to know a free way to do this. I preferably want to load the names and numbers using an Excel spreadsheet. I do not mind if I have to key all the information in again, however, to use a free service.