Voice dialing systems use speech recognition software. The simplest systems, known as “speaker-dependent,” are based on recordings called voice tags. To create a voice tag, the user says the words that will identify a contact — “Web Ad Services,” for example — and keys in the associated phone number. To call that number in future, the user simply repeats the words in the voice tag. Speaker-dependent systems can only identify numbers that have voice tags created for them and sometimes fail to do so when somebody other than the person who made the creative recording says them. Most phones with speaker-dependent systems support a limited number of tags.