San Francisco picked up Boldin from the Ravens for a sixth-round choice in the updating NFL draft, and sent Smith to the Chiefs and new Coach Andy Reid in return for an undisclosed 2013 draft choice -- but apparently not the overall No. 1 pick owned by the Chiefs -- and a conditional pick in 2014.
Boldin had 22 catches for 380 yards and four touchdowns in the last post-season. That includes six receptions for 104 yards and the first touchdown in Super Bowl XLVII, where the Ravens beat the 49ers 34-31.
Boldin was with Baltimore for three seasons after playing in Arizona for seven. He has 772 receptions for 10,165 yards and 58 touchdowns in 140 NFL games.
Smith had been the 49ers' starting quarterback until he was hurt last season and lost the position to Colin Kaepernick. With Kaepernick at quarterback, the 49ers advanced to the Super Bowl.
Smith, 28, was the first overall pick in the 2005 draft and passed for 14,280 yards and 81 touchdowns in eight seasons in San Francisco.
"We would like to thank Alex for his contributions to the 49ers organization over the past eight years," said 49ers General Manager Trent Baalke. "He is a true professional who represented the 49ers with class on and off the field."