Yes, you can often activate international roaming even after leaving your home country. For many providers, this can be done through their official mobile app, via a web portal, or by sending an email to the customer support team with your account details and request. Some carriers also provide specific USSD codes that can be dialed while abroad to enable the service. However, it is essential to check your specific mobile carrier’s policy before you travel, as some may require you to be connected to your home network to initiate the activation. If you are already abroad, check your carrier’s website for a "roaming support" email address or a self-service portal, as these are the most common methods for retroactive activation.