Euroboy,
I doubt whether phoning at 1050 to take you off a 1100 Sby is legal.
There is no doubt that roster stability is not only in the long-term interest of the pilot but also the airline. Some airlines have discovered that they have saved money by getting the roster stable and putting in block standby's.
If all fails get caller ID and don't answer the phone until you are either on Standby or close to leaving home. Alternately get a pay as you go mobile.
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