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Hello Tex,
Thanks for asking.
I don't own a Sony Ericcson 610 myself, but I think that you will most 
likely not be able to pair the device from the device's side alone. 
You usually will have to use OS X Bluetooth Assistant for this.
Suggestion: 
Use the Bluetooth Assistant (launch it through System Preferences or 
directly at /System/Library/CoreServices/Bluetooth-Assistant.app) on 
your Mac to pair a new keyboard and perform the steps you described on 
your mobile when the Bluetooth Assistant searches for devices.
Best regards, 
Felix Schwarz