(4) Time spent as an on-call fireman for a municipality, calculated at the rate of one year of creditable service for each 5 years of time spent as an on-call fireman, provided that (i) the firefighter has at least 18 years of creditable service as an active firefighter, (ii) the firefighter spent at least 14 years as an on-call firefighter for the municipality, (iii) the firefighter applies for such creditable service within 30 days after the effective date of this amendatory Act of 1989, (iv) the firefighter contributes to the Fund an amount representing employee contributions for the number of years of creditable service granted under this subdivision (4), based on the salary and contribution rate in effect for the firefighter at the date of entry into the Fund, to be determined by the board, and (v) not more than 3 years of creditable service may be granted under this subdivision (4). Except as provided in Section 4-108.5, creditable service shall not include time spent as a volunteer firefighter, whether or not any compensation was received therefor. The change made in this Section by Public Act 83-0463 is intended to be a restatement and clarification of existing law, and does not imply that creditable service was previously allowed under this Article for time spent as a volunteer firefighter.