Be aware that international roaming can be expensive, especially in Seychelles because of its remoteness.
With a local SIM card, like a Seychellois one, you can enjoy local rates, which are almost always lower than international roaming rates.
But you do need to buy a SIM card from one of the local mobile operators.
You can get a Seychellois SIM card for 100 SCR (7 USD) in Airtel and Cable & Wireless stores across Seychelles.
A bundle featuring 1 GB of data is available for as low as 200 SCR (14 USD).
You can get a Seychellois SIM card in the official stores of Airtel and Cable & Wireless
They are also available at Victoria/Seychelles International Airport.
Please find more information here : https://www.phonetravelwiz.com/buying-a-sim-card-in-seychelles-guide/#other-ways-to-stay-connected-when-traveling-in-seychelles