It could be just idle speculation at the moment, but The News Independent reports that there will be a Basic, Advanced, and Pro model released. The Basic model, which is unlikely to be called that at release, will feature 4GB RAM and 64GB storage space.
The Advanced is expected to feature 6GB RAM and 128GB storage space, and the Pro variant is tipped to come with 8GB RAM and 512GB storage space.
Microsoft is yet to comment on the existence of the Surface Phone, though CMO Chris Capossella has previously said that there's a need for a ‘spiritual equivalent’ of the Surface series of devices for mobile.
If this line does come out in March 2017, we should hear more official news in the coming months.