Unlock SonyEricsson / K500 / K600 / K700 / K700i / T68 / P800 / P900
For these models, you need a T28 datacable, the cheap serial port ones from eBay work the best. Download this software, and configure it as per the screenshot below, obviously selecting the correct phone model first.
You could tick the Read All Codes box instead, and input the codes manually. Don't use the Change IMEI option. It's illegal and worse still, it'll break your phone.
This software also supports a wide variety of other models:
K300, J300, K500, K508, F500, K600, K608, V600, K700, K750, D750, W800, V800, Z800, S700, S710, Z1010, Z500, T200, T202, T226, T230, T237, T300, T310, T312, T316, T610, T618, T628, T637, P800, P802, P900, P908, Z600, Z608, R520, T39, T65, T68, A3610, T100, T105, Z200, Z208, A2618, A2628, T20, T29