We use the mobile in question as our primary phone for about a week or so before sharing our verdict with you. We realise this isn't perfect, since there are some aspects of the device that don't become obvious during that time, and in an ideal world, we'd use every phone for a couple of months before we publish our review.
But we work under constraints where most devices aren't available to us for that long - almost all products that we review are loaned to us by companies for short durations - and there's also the competitive pressure of wanting to get your review out before others do, as long as it doesn't involve cutting any corners.