The two of you are talking about different kinds of GPS devices. Cell phones may well kill the modern GPS devices that are designed to give street directions and sit atop dashboards. I've used Google Maps on my e51 rather than a GPS unit for years.
They certainly won't, however, kill the standalone GPS units Duradin is talking about, which are designed for hiking, sailing, and other more rugged uses than simply driving through town. Google's new offering doesn't apply to those anyway: cell phones have been able to replicate the functions of such devices for quite a while. However, cell phones are, by comparison, incredibly fragile and inappropriate for situations where standalone GPS systems work well: many of my GPS systems are waterproof, and I've dropped one out of a moving car with no repercussions; buttons are often designed to be easy to use with gloves; battery life is significantly higher even when compared to a cell phone in airplane mode; and in general, these sorts of systems are being used where carrying around a cell phone would be completely useless due to lack of service.
There's the possibility that one could combine GPS and a satellite phone, but I don't think the result would be popular. To begin with, if one falls out of a canoe, or off a cliff, or just breaks, it's nice to have lost only one of two.