Htc desire c locked on three

I have a htc desire c, is there anyway of unlocking it to work on any network as I'm in uk the phones on three network I need it on Vodafone, I tried the hold the power on button and volume button but that's done nothing, phones just working on three network only, I've search and search on how to unlock this but I only have a iPad no laptop so have I got no chance??

Thanks for reading guys.

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