A2billing Customization

Our project is A2billing . we need a programer to customize A2billing with the following: changing WEBUI LOGIN in cutomers tab to ACCOUNT NUMBER for registration. infact at this present time , All Customers use this field : (ACCOUNT NUMBER ) for account number in their IPphone devices and softphone. we want to our customers register their extentions by WEBUI LOGIN not ACCOUNT NUMBER . By this way we can create any extention bye any prefix . for example an extention can strart with this prefix:11111XX . Moreover we need a programer to design voice mail and sms services for A2billing software.