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No, you can even unlock the iPhone when Jailbroken.
Not unless you want to lose your unlock
No, you will only lose like your music, photos, ringtones, contact and what ever iTunes offers to sync. Restoring to a previous backup can probably lose your jailbreak. Restoring your device completely removes your jailbreak.
If you update your iPhone/iPod, you will remove the jailbreak, then you would have to wait until the jailbreaking websites invent a jailbreak for the new ios, but why update if you jailbroke it?
No.
If the info is already saved on the device, yes, just don't do any updates or you will lose everything and the unlock.
Any time you restore an iPhone you will lose your jailbreak and your unlock and you will have to start from scratch and do it all over again. You also cannot use a Boost SIM card in an iPhone as Boost is owned by Sprint/Nextel and their SIM cards use iDEN technology, not GSM. The Boost SIM cards can be used for International Roaming only and will not work on GSM networks in the US.
If you jailbreak correctly, no, you keep all your songs on your ipod after jailbreaking.
nah
If you have Cydia then there is no point to re jailbreak. If you try to re jailbreak, The tool you try to use will not let you jailbreak it because the Cydia sources are already installed into your device.
Yes but you will lose all the jailbreak features.
I suggest you go on mobile me