Smith, who led the NFL with a franchise-record 107 receptions for the New York Giants in 2009 and made the Pro Bowl, will be entering his sixth season. Last year he caught nine passes in 11 games for the Eagles before being sidelined by a knee injury.
Smith was a second-round draft pick in 2007 and had five catches for 50 yards in the Giants' Super Bowl victory over the New England Patriots. He has 231 career receptions with 12 touchdowns.
Miller enters his third season with St. Louis. In 2011 he played 12 games and had nine special teams tackles.
Mulligan was with the New York Jets the previous three seasons. Last season he started nine games and played in all 16.
Ojinnaka was in training camp with the Rams last summer and then signed with the Indianapolis Colts, starting three times and appearing in nine games.