As stated above, Squawking 7600 will highlight your plight, D&D will try and contact you on 121.5. Your sat phone works indepently of your radios and in the situation you described, you should phone D&D on the published number. You can then state your intensions and the wheels will grind into motion. This number is valid throughout the world and yes it has been used by aircraft well outside the UK FIR.