I have the basic talk/text with voicemail now. Costing me $36/month. If I upgrade to the $39 plan now, with my old flip phone, can I then go into the store in 2 weeks and pick out a new phone and use it with my upgraded plan? I am going on vacation and won't be able to use my new phone for a week, but I don't want to miss out on the $39 deal. I also want the 14 days to fully test it out.