Which device do you have the SIM installed in? I used to change out devices so often that my 8700's SIM holder eventually started getting loose. So anytime I would so much as smack my hand on it, I would get SOS. If I smacked the other side, it was fine.
If you fall out of the network and don't roam into another one then yes, that is probably why it keeps cutting in and out. However, that means you would have to be totally out of cell tower range. I've never been on a boat with my bb so I don't know how far you would have to be offshore for you to have no cell tower access.
I get the SOS when I go into my bathroom. My signal is awful in my apartment. Mainly it just means that your voice and data signal is extremely weak or non-existent in the area you happen to be in. However, you're still able to make 911 calls in this mode. If you have a lot of metal in your walls or basically any wireless signal blockers...the more you have, the worse your signal will be.
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