CRA finds that the two-out-of-three telecommunications GST place-of-supply rule overrides the general rules

ETA, s. 142(1)(g) deems a supply by a registrant of a service which is partly performed in Canada to be made in Canada. However, s. 142.1 provides a "two out of three" rule for deeming a telecommunication service to be made in Canada  - for example, in the case of a telephone call, if two of the following are in Canada: place where the call is emitted; where it is received; and the billing location. CRA considers a telecommunication service, that is not deemed to be made in Canada under this rule, to be made outside Canada, even if that service is partly performed in Canada.

Neal Armstrong. Summary of CBAO 2014 Roundtable, Q. 27, under ETA s. 142.1(2)(b).