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Guessing that you are trying to 'bring your own phone' over to Spectrum 's cellular service? Maybe you could tell the forum readers what you mean by APN numbers and why you need it/them. I've worked for a major player in the cellular industry for over 30 years and never heard that term used before. Today brings an opportunity for me to learn something new.
APN stands for Access Point Name. APN settings are set up to allow a device to access data over the mobile network. These are set automatically by the carrier and the only reason I can see why someone would want to change them is to attempt to bring your own device to the network without actually "activating" it properly.