I got the 20GB/65$ plan (BYOP, rentention/loyalty). I strongly recommend doing the Change with a human advisor, since the self serve route might remove the addons (in my case, it almost removed the now 7$ iPhone Visual Voicemail addon). As for your credits, you might lose them no matter what you do if you change plans. I lost my free iPhone VVM I changed a previous time. It goes without saying (and you did mention it), read the fine print. For example, you might get or lose the 5h of unlimited downloads. EDIT : I recommend BYOP, to reduce the monthly bill and to have more leverage during negotiations.
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