Can I unlock my mobile phone so I can operate it without a SIM?

[Jamie T]

I still use it for music because its very good sound quality but have brought a new mobile as part of an upgrade. To transfer songs i have to take the SIM out of my new phone and put it in the old one so I can use it with my PC. Is there a way around this because I dont like constantly taking my SIM in and out. BTW both phones are sony ericsson.