Can I use my trusty ole Razr with my current ATT wireless service?

Can I use my trusty ole Razr with my current ATT wireless service?

I'm unhappy with voice quality of my pantech so I swapped the chip back to my 10 year old Motorola Razr. After a full charge it come on perfectly, I put in my PW and it showed 'registered' with my correct phone number. I tried calling out but it always "Failed' to connect. what can I do to get it to connect the my ATT service and work?