The following is a harrowing tail of the effort required to simply activate a Nexus 6 with Sprint in the US. Hopefully, if someone runs into a similar situation, they can stumble upon the post and save themselves some time...
I recently purchased a Nexus 6 from Motorola's Website to replace my aging (and misbehaving) Nexus 5. As the Nexus 6 will run on most any network in the US (as did the Nexus 5 before it) I didn't think anything of grabbing one from Motorola directly so I could get the white 64 GB model.
When the phone arrived, I pulled it out of the box, looked at it, realized it took a Nano SIM (my Nexus 5 uses a Micro SIM) and promptly headed for Sprint so I could get a SIM and get the Nexus 6 activated while I was at it.
I got into the store after waiting several minutes for them to unlock the door (promptly at 10:00am local time), informed a helpful lady that I needed to activate my new phone, and went back to a desk to start the process.
She took my account information and the phone, scanned the phone in several times, looked at me with a puzzled expression and asked me if it was a Sprint phone, to which I replied it's an unlocked phone and will work on just about any network just like this one, at which I held up my Nexus 5. She spent several more minutes fumbling around before asking me if Motorola could've sent me the wrong phone because her system wouldn't accept any of the numbers on the phone.
I stepped aside and called Motorola, got bounced around their phone tree for a few minutes, and ended up in Sales Support, where I explained what was happening to the man on the other end of the phone who asked me a couple of questions about what was going on and then informed me that they could not force Sprint to activate a phone if they were refusing. I tried to explain several times that Sprint was not refusing; that, rather, they were unable, before getting fed up and hanging up on the man.
While all that was going on, I grabbed a store phone and did an Internet search and promptly found the solution which was quite simple: Use the IMEI number on the box minus the last digit which is what Sprint knows as the MEID number (thanks Android Police!). I went back to the nice lady that was helping me with this information and it worked like a charm. Then came the SIM...
The nice lady discovered I had no SIM and promptly told me they didn't have those types of SIMS. I told her yes they did, they're in Nexus 6es as well as iPhone 6es and, I'm sure, many other phones. She responded that Sprint didn't even carry this phone (the Nexus 6) to which I, of course, said "Yes. You do." She proceeded to argue with me until I walked her over to the Nexus 6 on display 20 feet away from us. At that point, she disappeared into the back of the store and, supposedly, rummaged around until she found a returned Nexus 6 from which she was able to scavenge a SIM. She plugged it into the system, slid it into the phone, and handed it to me with instructions to let her know if I had any problems.
So, the moral of the story? Neither Sprint nor Motorola was able to tell me how to activate a Motorola phone on Sprint's network and Sprint didn't even know it sold the thing or that it had nano SIMs and I, the consumer, would've walked out of that store and promptly returned the Nexus 6 had I not happened to be a tech expert who really wanted my new phone to work and absolutely knew it was possible.
If Motorola and Sprint want to continue doing business, they should probably be sure their employees have basic information like how to activate phones at their disposal....