Collecting phone numbers at your brick and mortar place of business is as simple as filling out forms or collecting business cards, but what about online? Again, that can be as simple as asking customers to email or text you their information, or you can go high-tech and actually set up an online form, linked from your website, Facebook page, or even advertising links.
Marketing through cellphones' SMS (Short Message Service) became increasingly popular in the early 2000s in Europe and some parts of Asia when businesses started to collect mobile phone numbers and send off wanted (or unwanted) content. On average, SMS messages have a 98% open rate, and are read within 3 minutes, making it highly effective at reaching recipients quickly.
Once you've collected your mobile numbers, verified that you have followed all of your legal responsibilities you can start your SMS marketing campaign. I'd suggest using a 3rd party service provider to ensure that you are able to track the return on investment for your campaign, embed an unsubscribe message, and easily manage your SMS marketing database including unsubscribes.