They got took out after the first update the preset one we had. But From what I read you would just need to change it from ipv4 to ipv6. But since you can't edit the existing one or copy it.
You can try these custom apn settings..
Connection Name : T-mobile IPV6
Internet APN
Access point name : epc.tmobile.com or fast.t-mobile.com
Username : Blank
Password : Blank
Proxy Address : 216.155.165.50
Proxy Port : 8080
Network Type : IPv4 (IPV6)
Authentication Type : none
MMS APN
MMS access point name : epc.tmobile.com or fast.t-mobile.com
Username : blank
Password : blank
Proxy Address : 216.155.165.50
Proxy port : 8080
MMSC address :
http://mms.msg.eng.t-mobile.com/mms/wapenc
Network type : IPv4 (IPV6)
Authentication type : none
save
activate apn
Restart Phone, Check Cellular Network Selection for T-MobileIPv6
Check Internet, email, internet sharing, MMSC has well..
swap epc to fast.t-mobile.com has well if something is not working..