That phone (often or always) comes out of the box set up to connect to the Yealink provisioning service (which yes will give you dial tone) but it has nothing to do with your SIP service you want to use or any dial tone that's useful for making calls.
To reset your T4 series handset, ensure your phone is at idle (no calls in progress, or any notifications for voicemail, etc.) Press and hold the OK key for about 8 seconds, until you receive the 'Reset to Factory' prompt, then press OK to confirm the reset.
If it just reconfigures the same way then you have to contact Yealink and get them to remove it so you can configure the phone manually the way you want to. I think you might be able to get into it for a short time after resetting it with the standard admin/admin login and then turn off auto-provisioning but when I did that it still went back to the provisioning service eventually until I asked Yealink to exempt it.
Cisco phones you need a dedicated server in an enterprise environment
Not entirely true, I have gotten them to work nicely with FreePBX but it's probably not how you want to be spending your day and they are meant for a Cisco server so you have to manually create some required configuration files, etc.
VOIP service from my service provider
I'm thinking you might not have a VoIP service to use this phone with because you say you converted your phone to digital and plugging a standard phone to the FON port works, also that you expected it might work out of the box without any configuration leads me to think you don't have a VoIP service, just what your provider calls digital. and digital does not always mean SIP (at least not a SIP service you can use except by plugging in an ancient analogue phone).
In any event, if you did purchase a SIP service from someone they will have given you the information you need to configure that phone to work with it.