Adding Service Days
I still have 46000 minutes but no service days. Can I buy service days only.
No, I don't believe that NET10 has a card you can buy simply for adding service days.
Sometimes, if your phone hasn't been active for a while, it will display an absurdly high number of minutes such as 46,000 (I'm guessing that that's the case here). This is due to some sort of glitch. You need to re-activate the service with a new airtime card, but I don't believe you will retain those previous set of minutes.
On the other hand, if your phone's service ran out recently, then if you add airtime again, you can keep the balance you had before.
Note: Tracfone does have a service where you pay six dollars a month to keep your phone active without adding any airtime.