Personally I think the phone company's used a poor selection of title for this. Basically: Activate today means the phone comes to you with the SIM card installed. Example would be if you say have AT&T. You want to upgrade to a new phone. It gets mailed to you. It has the SIM card installed for AT&T. When you have the time you activate it. Activate Later essentially means the phone comes without a SIM card. You need to contact the provider and set up service and they will give you a SIM card to install. Then you activate your phone.
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