First of all try this site, this is the Sony ericcson official software update service:
seems they also do firmware updates for the t610
*www.sonyericsson.com/spg.jsp?cc=au..._1_3_1_1&zone=ps&lm=ps1_1&pid=10055&fid=21839
There are also paid services that usually do remote unlocking/updating of firmwares.
Like this one:
*www.unlockitnow.com/remote/Firmware_Upgrade/Sony_Ericsson/flash/T610_Firmware_Update.php
this one costs around 35 $ provided u have the data cable that they mention.
Plus keep one thing in mind, messing with the firmware is a dangerous thing and if something goes wrong during the process, there is a possibility you could kill your phone.