The move was announced Tuesday after the team placed rookie guard Eric Wood on injured reserve. Wood broke two bones in his left leg in an 18-15 loss at Jacksonville on Sunday.
Simmons is an eight-year NFL veteran who joins the Bills (3-7) after being released by New England on Nov. 9. He appeared in one game for the Patriots this season.
Selected by Pittsburgh in the first round of the 2002 draft, Simmons started 80 games for the Steelers before being waived in September.
Buffalo, which hosts Miami (5-5) this weekend, also lost reserve lineman Seth McKinney to a season-ending knee injury on Sunday.