Stmav, Nokia does not like the US based CDMA carriers, and Nokia needs them in order to make themselves a serious OEM (just sticking with Verizon and two GSM carriers does not make them competitive, especially when the sales for the Lumia 822 on Verizon have been atrocious, and had to resort to offer them FREE).
Sprint's network is being seriously improved (if you actually follow the data a site named S4GRU.com provides, which happens to be right on). Still some work to do i. Many markets but it's moving, and just before we go into another Sprint bashing, take a look at AT&T's network which is about 2-3 years of needing a complete overhaul as the one Sprint is doing. Patching as AT&T is doing will only for for so long.