Both IRIDIUM satcom and Inmarsat satcom can not operate simultaneously, whenever you use either one kind of satcom, you shall power of another one.
if you have a decent installation, then INMARSAT filters should be installed, if also Iridium is installed...then it will work without a problem..
if those installation basics have not been followed on the bird you fly, I would, if I were you, not even trust, whether the oil in the engines or the toilets have been serviced correctly...