Need advice for selling iphone 5 and getting iphone 6 plus?

I have a 16 gb unlocked iphone 5 that runs on tmobile right now. I was wondering what's the best option for me. I think I want verizon because I'm joining the Air Force soon and I need good coverage. They have a plan where they take your old phone and give you iphone 6 for free if you renew 2 year contract but I'm not sure if it works for new customers. They have a edge program that looks really good it's $50 a month for 2gb of data?! I was thinking should I wait or is this a good opportunity for an upgrade?

Is this iPhone locked or unlocked?

I'm selling my iPhone 4S and it used to have a postpaid sim. I transferred the postpaid sim to my new iPhone, and put in a prepaid sim into my 4S. It's from the same network, except that its new sim is prepaid, but it does work. So, does that mean it's unlocked?

How to download music free to iphone?

I have an iPhone5c and I don't really wanna spend loads of money on iTunes buying songs because I quickly get over them and end up deleting them so it's a waste really. I was wondering if there was any apps or methods of getting free music but so it'd download in my music file with my iTunes music just so it's easier and I won't look poor.

Whatsapp backup to a new number?

I want help with whatsapp.
I recently deleted my Whstapp app for some reasons but i backed up the chat & history in the Icloud backup and now i want to install Whasapp again and want to have that backup but on a different number other than i was using before. Suppose i was 17652xxx before and now i wana use my another number 17636xxx. I have the old sim also which is working but i wanna have the chat backup in the whatsapp with the new number. I'm using the same phone as i was using before, my Iphone 4… Is it possible guys? Need help… Thanks in advance…

Should I buy an iPhone 6+ from the US or UK store?

Should I buy an iPhone 6+ from the US or UK store?

Added (1). I'm planning to upgrade from an iPhone 5 to an iPhone 6+ (64 GB). I live in Qatar and it's generally more expensive here upon release, so I'm thinking of preordering my phone. Question is, should I buy it from the US or UK store? I'm not from the US so I most definitely need an unlocked phone without ties to any carrier. I usually check the model number of the phone for the GSM and LTE compatibility (Bands 8 and 20) in my country.

Added (2). Sorry, the LTE bands are 7 & 20 NOT 8 & 20