Does DDNS really work when you are using Safaricom 3G?

My tests indicate that it doesn't work, unless setup imenishinda aki, which I highly doubt.

I can see the DDNS server sees my IP, but connecting back to my IP doesn't work, even just ICMP (and don't suggest I check my firewall because I have).

Safaricom must be blocking such a possibility and so might be wanting me to ask them for a routed APN, right?

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