I looked at this some time ago and, as I recall, it is NOT required anywhere in Pacific (well southern anyway, I didn't look north) for RNP10. However if you want to get 30nm separation applied, you must be RNP4 and have a direct/ immediate way of communicating with a controller, which is CPDLC (or VHF). SELCAL on HF doesn't count. ICAO doc 7030 - regional procedures I think has the gen.