AFAIK the iPhone is capable of both 800 and 1900 MHz operation on Sprint. This has to be the case as there are many areas in which 800 is used to relieve excessive volume on the 1900 band. In addition, the limitation in cellular data does not lie with the carrier frequency, but rather with the limitations of CDMA, how much traffic that tower was designed to accommodate, what the status of the backhaul connection is, and of course signal quality. In fact, Verizon's admittedly blazing fast LTE runs on the 700 MHz carrier frequency which used to belong to analog TV signals. Now, you may notice that in some places you may be able to lock on to a signal much better indoors than in others. This is because signals sent at a lower frequency (800 MHz vs 1900 MHz) have a higher building permeability. Obviously data speeds at 4 bars are going to be better than with one bar so where you have 800 MHz service you might notice SOME difference. 800 MHz is a little bit rarer to come across and is mostly used in dense areas to alleviate traffic on the 1900 MHz band.
I've seen this issue myself on my iPhone and I've seen this complaint by many in various places on the internet. Sprint has not said anything specifically. However, there was a leaked Sprint document (no I didn't leak it. That memo was not even intended for anyone in the retail channel) that suggested that there would be a fix for it soon. For now, we just have to sit and wait and be patient. We have to trust that the issue is being worked on and that both companies are understandably trying to avoid bad press. Try to use WiFi whenever possible.