Is it possible to have a Virgin Mobile Iphone 5s, moved over to Sprint Contract?

No. It's locked permanently to VM.

Virgin mobile told me a few days ago that they will "unlock" it after ONE YEAR of service, on request.

Then their policy has apparently changed in the 2 1/2 years since this thread was last active...

I think the phones are the major change. (And the fed regulations that require ability to unlock. ) VM phone was so much less expensive I thought I'd try it for iPhone - it's been fine for little flip phone over the years. Too new to judge, but so far, ok service + nice tech support

There are no federal regulations requiring carriers to unlock phones at all. There is a voluntary agreement among the major US carriers that they will do so. They entered into this agreement specifically to avoid regulation of the issue by the government.

Virgin Mobile is NOT a signatory to the agreement in question. They are under no legal obligation to unlock phones at all.

Interesting. Voluntary compliance is an iffy thing . I do have it in writing that they will unlock it after one year. Time will tell!!!