This is a very interesting suggestion. I see now why people just sign up with carriers, it's confusing as hell trying to determine if XYZ phone is compatible with Solavei or whether you'll get 4G speed, and even then your choice of phones is limited. The phone specs are confusing. Some Galaxy S III specs say dual-core, others say quad-core.
And buying the Nexus 4 from Google Play is confusing. I see no way of knowing if the phone would be compatible with Solavei, or if it comes with a sim card, or what it would cost to buy it separately.
So it seems like there is some risk involved with purchasing a phone on the internet, you may not get what you really want/need. That risk is minimized when you walk into a Sprint store.
I went into Sprint the other day to look at the Optimus G. I didn't like the feel of the phone in my hand. There were no phones I really fell in love with. iPhone 5 has a smaller screen than my Galaxy S! They had Galaxy S III but eh, it's blue!
The Sprint guy wanted to make a deal badly. On the Galaxy S III they were asking $199 each with 2-year deal. The guy said he would give me $44 for my old Galaxy S and then after I didn't pull the trigger on that he said he would give me $100 more off of each Galaxy S III (my wife and I would have a shared plan). So I could have had Galaxy S III for $55 each with 2-year plan (TODAY ONLY!!!), vs. $575.00 each from gsmnation.com with Solavei sim card. The plan (for my wife and me) would be about $160 per month on Sprint vs. $98 on Solavei. So over a 2-year span I might save about $450 with Solavei, assuming we had no problems with the phones, etc. And of course Sprint would manage transferring all the data, contacts etc. from our old phones to the new phones, that's worth something.