Both iMessage and FaceTime will use your primary phone number and Apple ID email addresses to send and receive. GigSky SIMs are data only and don't have an associated phone number. However, you can still use iMessage and FaceTime using GigSky data. You just need to make sure that you deselect your primary phone number in the Settings while you are using GigSky rather than your primary service.
1 - Select your GigSky eSIM for mobile data
2 - Go to Settings > Messages:
3 - Turn iMessage off:
4 - Turn iMessage back on:
5 - Tap Send & Receive:
6 - Uncheck your primary phone number by tapping it and make sure that your email address(es) are checked. This ensures that you will be able to send and receive messages over the GigSky data connection using your email address. Do not select the entry for your GigSky eSIM:
When you want to return to using your Primary SIM, go back to the Send & Receive section and tap the entry for your phone number to select it for messaging.
1 - On your iOS device, tap Settings > FaceTime and switch FaceTime on.
2 - In the section "YOU CAN BE REACHED BY FACETIME AT", uncheck your primary phone number by tapping it. Make sure that your email addresses are checked. You will then be able to make and receive FaceTime calls using your email address and GigSky mobile data. Do not select the entry for the GigSky eSIM.
When you want to return to using your Primary SIM, go back to the FaceTime settings and tap the entry for your phone number to select it.