Easter Island is a part of Chile. T-Mobile's web site (and prior experience) told me coverage was included in Chile. But Easter Island was not listed anywhere separately by T-Mobile.
nce I got to Easter Island I discovered that our US phones refused to roam on either of the cellular networks there. Attempts to join the networks were rejected, so I never had the opportunity to pay an unreasonable rate for service. I didn't bother with a local SIM. With offline maps I was at least able to use our phones for navigation.