Until then, cell phones were used to make calls and to receive voicemail message alerts. Americans used cell phones to send just 0.4 SMS per month, but that all changed in 1999. Once messages could be sent and received between different network providers, the average user found that sending SMS was more convenient and there was added value for consumers. In 2000, the average number of text messages sent in the United States increased from 0.4 per month to a whopping 35 text messages per month per person in the United States. Initially, SMS was based on the multi-tap system where each number on the phone was linked to three or four letters that you had to tap multiple times to write the words in the text. This method was time consuming and was probably the first step leading to the SMS vocabulary we see in use