This paper analyzes the influence of impulse noise impairments in a telecommunication channel on the speech transmission index (STI) value, which was measured using RASTI method. So far STI has not been applied in telecommunications as a speech transmission quality measure. Impulse noise components were formed as IEEE standard impulse streams. Impulse noise amplitude level relative to the level of reference (RASTI) signal as well as the duration between successive impulse events were varied in a channel. Consequently, STI value was determined as a function of these two parameters. In the same channel PB-Word Score evaluation was also performed. As a result, the correlation between PB-Word Score and STI value for a telephone channel with impulse noise impairments present was established in this paper.