How do I best validate my idea?

I'm traveling and I came across a problem that needs a solution. Now, I'm sure once this problem is solved it will benefit a lot of people. I'm thinking of providing a service to a major company to offer to its customers. After speaking with one of the staffs from said company, they told me that the service they once had did not work. It sounds to me that they did attempt to offer similar service but things did not work out too well. The service I want to offer will be best provided via mobile phones. Sort of like a text sent to people to remind them that they balance fee for their prepaid and monthly account is low. And that, they need to recharge their accounts to get service provided by the major company. I also think the service offered by us may have to be sent via the company or through some kind of way. I hope I've made myself clear and my apologies if I haven't provided enough info. Please, keep in mind the topics provided for this question may be inappropriate. I'm unsure of service.