S-ON/OFF question.

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http://androidforums.com – I will be getting my evo soon however I don't have a spare cable around to do the s-on trick or I would do it as soon as I unbox the phone. (I see mixed opinions about using a paper clip so I'm kinda scared to use that....) I'm gonna have to stay S-ON for a bit starting off for a little while. With 4EXT, can I go into the sprint's XDA CDMA HTC Evo 3D section and flash whatever rom? Or do I have to stick with the roms that specifically say virgin mobile? I would really like to slap MIUI within minutes of opening it (General)