Z310 has a different platform than the "usual" other phones. It's PNX5230, not DB2010/12 or DB2020.
The only server I saw that offers unlocking is davinciteam. But you should write them a mail first to ask them. On the Z310i site they offer unlocking but PNX5230 is not listed in their price table.
If they do not unlock it, you should find someone with an SE Tool Box or with Cruiser Plus. Buying one of these tools would'nt make sense just to unlock 1 phone.