Hi @johnb.7fad6b and welcome to the Member Community. Sounds like your new phone is active on the GSM network (T-mobile) and your old phone may have been CDMA (Sprint). Here’s an article to see if new phone is active on GSM or CDMA.
If you’ll share just your zipcode (nothing else) others in the community can help you determine which network has the best coverage for you.
If CDMA is best, and your new phone is on GSM, here are instructions for obtaining a CDMA SIM. Moving CDMA SIM between phones is not recommended.
Here are instructions for activating a cell phone if you decide that you just want to go back to your old phone. Scroll down to the How to Activate a Cell Phone tab, select the I’m Activating on an Existing Account and follow the steps.
This is a two prong approach. One to see if a change in GSM vs CDMA is a possible issue with the new phone. The second is to reactivate old phone.
A lot of information, but want to give you options. Please come back if you have questions.