I used to have an iPhone, switched to the Lumia icon and now no one receives my texts and I can't receive theirs unless they have a non iPhone device. Any ideas how to fix this?
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Are you sure that they're using the standard SMS and not the iPhone/Apple specific app? I know that some of my family members who use iOS exclusively had the same problem and we found that they were using an iOS to iOS texting app (iMessage, I think) and not the standard one. Once they used the other app, we could communicate via SMS.
I'd give Apple and call and tell them that you've switched away from an iOS device and to have you're iMessage cert removed from the Apple server. It won't solve your problem instantly because it takes a bit for the server to purge the cert. It may take up to three days for everything to clear out.