Try Visible Free Before You Switch

Visible lets you trial the service on your existing phone before porting your number, with no credit card and no commitment. It runs as a second eSIM line alongside your current carrier, so you can test coverage and speeds where you actually live and work rather than relying on a coverage map. That is the sensible way to evaluate any carrier that leans on network prioritisation, since real-world performance at busy times is the thing a map cannot tell you. Requires an eSIM-capable phone.