I don't think corporate stores should charge you for the CDMA to GSM switch. I understand if they charge you for the SIM card, but a little persuasion may get them to lower or waiver it. With that amount of credit, I would get the LG Leon, pay a bit to get it unlocked and sell it. I can see a quick $80 for it for someone from T-Mobile being able to use it. For phones, I would recommend the One Plus One. I know their tactics for sales aren;t so great, but they now have it available with a price cut. They should support the phone for a long time, so for $250 (plus fees) you will have a long lasting phone.