blackberry curve 8900 *

Selling a blackberry 8900 bought it a month ago needing a battery I have just replace the full housing and covers so looks like brand new, screen is scratch free costing (45) Replaced the battery with a brand new one (6) unlocked to all networks (10) work with vodaphone/orange/t mobile/o2 etc looks like a new phone can show it working now after all the money spent it worked for a few weeks now when i make a call it says call failed. BBM AND INTERNET STILL WORKS FINE need another phone with wifi......