According to Wikipedia, “Short codes (also known as short numbers) are special telephone numbers, significantly shorter than full telephone numbers, that can be used to address SMS and MMS messages from certain service providers’ mobile phones or fixed phones.” You have to pay to get a short code, and relatively few people or organizations have them. After they give out the 100,000th of them, I don’t know what will happen, but I suspect there are relatively few in use, so maybe it’s not a worry.