I have this same problem with my 5c. I recently repaired a phone that is locked to ee. Me being on ee thought I could use this phone but I kept getting searching and occasional signal. I rung up ee and they to me that because I have a T-Mobile SIM card I have to get the phone unlocked which they won't do as its a second hand phone. Does anyone know if getting it unlocked will fix this searching problem as I am unsure?