The grammar of the speech input to a voice service system is normally specified by the voice service system. However, this can produce problems in respect of idioms, such as dates, which are expressed different ways by different users. To facilitate the handling of idioms, a user is permitted to specify their own idiom grammar which is then used by the voice service system to interpret idioms in speech input from that user. Typically, the normal grammar of speech input is specified by grammar tags used to mark up a voice page script interpreted by a voice page browser; in this case, it will generally be the voice browser that is responsible for employing the user-specified idiom grammar to interpret the corresponding idiom in the speech input by the user. The user-specified grammar can be pre-specified directly to the voice browser by the user or fetched by the browser from a remote location on the fly.