Missus and I want to take our mobile phones to Singapore.
Will only use them to call each other (or text) when not together.

Telstra shop "gurus" keep waxing on about replacing sim cards or calling
back to Aus.

Am I wrong to assume that after I get Roaming "activated", and amend our
mobile numbers to the required
+61 and drop the first O, that we just call each other, and eventually pay
the extra fee for the call being handled by Singtel to Telstra and then
back from Telstra to Singtel?

The "guide" from Telstra deems to suggest that Singapore charges are made
up of:
National Call
Call to Aus
Telstra charge to receive
Call set up fee
Incoming call

?????