iPhone (Single or Dual eSIM)
Open Settings > Phone > Call Waiting
Toggle Call Waiting ON
If you donβt see the option:
β’ For dual SIMs/eSIMs: switch to the active line under Settings > Cellular > tap the line > then check Call Waiting.
Android (Steps may vary by model)
Open the Phone app
Tap the 3-dot menu > Settings > Supplementary services
Select your SIM or eSIM
Toggle Call Waiting ON
Dual SIM/eSIM users: repeat for each SIM line if needed.