Voice based BPOs require speaking directly to customers either through outbound calling process or via inbound calling. for example on the phone, which could be a job in the form of a sales or support. Nowadays, voice process is also about instant live chat, voice chat, and the use of other technological platforms.
On the other hand, Non-Voice based process consist of back office work and other works that do not require one to one interaction with your potential customers. However these jobs may include computer work such as a payroll or analyst position. It includes official work that may include creating reports, preparing spreadsheets of daily sales, data entry in a particular software etc. For non-voice positions one must have profound writing skills and good computer skills i.e he/she should have complete knowledge of the office applications such as MS Word, MS Excel. Back office job requires you do the job fast and with minimal or no errors.