im new here,and i need help

[my3rd]

hi im new here,im from the philippines my cousin gave me t-mobile mytouch 4g from america,i use to open line it to a technician and it works,but sometime i cant make outgoing calls and sms,the message says mmi code something like that,it is also safe to upgrade it the newest update?thanks wish you can help me with this matter,thanks and more power...