What device? It seems unusual that there is some arbitrary maximum call length but I don't think this is the first time I've heard of this.
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Welcome to Android Central! I've seen this mentioned before -- just do a search for "4 hour cell phone call," and you'll see a lot of questions about it. It seems that wireless providers have an arbitrary 4 hour limit to a call, which is probably in case people accidentally forget to hang up on a line that's on hold, as well as to discourage extremely excessive network usage.