<PAGE>   1





                         CLASS A AND CLASS B SHARES OF

                         AIM GLOBAL INFRASTRUCTURE FUND
                  (A SERIES PORTFOLIO OF AIM INVESTMENT FUNDS)

                       Supplement dated October 16, 1998
                   to the Prospectus dated September 8, 1998


Effective October 19, 1998, INVESCO (NY), Inc. will resign as (i) sub-advisor
and sub-administrator to the Global Infrastructure Portfolio (the "Portfolio")
and (ii) sub-administrator to AIM Global Infrastructure Fund (the "Fund"). A I
M Advisors, Inc. will continue to serve as the manager and administrator for
the Fund and Portfolio.






<PAGE>   2



                                ADVISOR CLASS OF

                         AIM GLOBAL INFRASTRUCTURE FUND
                  (A SERIES PORTFOLIO OF AIM INVESTMENT FUNDS)

                       Supplement dated October 16, 1998
                   to the Prospectus dated September 8, 1998



Effective October 19, 1998, INVESCO (NY), Inc. will resign as (i) sub-advisor
and sub-administrator to the Global Infrastructure Portfolio (the "Portfolio")
and (ii) sub-administrator to AIM Global Infrastructure Fund (the "Fund"). A I
M Advisors, Inc. will continue to serve as the manager and administrator for
the Fund and Portfolio.



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