Kaber, a left-arm wrist-spinner, has been part of MI Cape Town squads for the last two seasons, including the the title-winning campaign in season 3.
The 33-year-old has good record in the shortest format having taken 61 wickets in 57 matches at an average of just and 20 and an economy-rate of just above seven to the over.
Kaber join a strong contingent of spinners at MI Cape Town with Rashid Khan, George Linde and Dane Piedt already in the squad.
Proteas spinner Shamsi was bought for R500 000 by MI Cape Town in the auction that was held in September but has pulled out of the tournament.
Shamsi had previously represented Joburg Super Kings last season and Paarl Royals for the first two seasons of SA20.
The fourth season of SA20 kicks off on 26 December when defending champions MI Cape Town take on Durban's Super Giants at Newlands.
Kane Williamson has rejoined Durban's Super Giants ahead of the fourth season of SA20, the New Zealand batter replacing Bangladesh spinner Taijul Islam, who is not available.
Jason Smith is relishing the prospect of returning to Newlands after being purchased by MI Cape Town at the player auction ahead of the fourth season of the SA20.
Dewald Brevis says he is keen to start a new chapter in his hometown after becoming the most expensive player in SA20 history after being bought by Pretoria Capitals for R16.5 million at the player auction.
Pretoria Capitals forked out a record sum of R16.5 million to acquire the services of Proteas batter Dewald Brevis at the SA20 player auction held in Johannesburg.
