Sprint reported record activations the day it started selling the iPhone 4 and 4S, but has that influx of data-hungry smartphones hosed the carrier's network?

According to TheNextWeb, an internal email sent to Sprint representatives says that Apple and Sprint are working on a fix for a "confirmed nationwide issue" regarding slow data speeds, but additional details were not divulged.

Apple iPhone 4S users have taken to the Sprint forums to complain about network speeds that are "too slow to be useful." Those who have contacted Sprint's customer support were told that it was a "known issue" and that a fix was on its way.

One user, jd_pruitt, used the SpeedTest.net app to measure speeds near the Denver, Colo. area, and recorded download speeds of 0.03Mbps and upload speeds of 0.06Mbps. Another user, some1nOC, had similar results in Orange County, but has "seen a big jump in the download speeds" over a three-day period. Download speeds on October 16, for example, were at 0.09Mbps but jumped to 1.35Mbps by October 19.

For comparison, I used the same app to test my AT&T iPhone 4 in New York City, and got download speeds of 3.44Mbps and upload speeds of 0.26Mbps.

"When listening to Pandora the stream would stop for a few minutes and start again," jd_pruitt wrote. "Browsing is noticeably slower from my former carrier AT&T. Translation: Yeah, it's pretty lame."

In a statement, Sprint said iPhone performance on its network is "consistent with our expectations." The carrier said it conducted benchmarking tests that compared its iPhone to those from other carriers and found "little to no performance difference."

"We are seeing a very low return rate for this device but we are watching the reports of speed issues very closely," Sprint continued. "We do see opportunities to optimize performance, specifically in high network capacity areas. We see this as typical optimization work and do not have any specific area of concern. Sprint is committed to providing the best possible experience for our customers. We are listening to our customers and working closely with our partners at Apple to ensure optimal performance of iPhone devices on our network."

In reviewing the Sprint version of the iPhone 4S on launch day, PCMag mobile analyst Sascha Segan found that "all of my Sprint phones were crawling along at a pathetic 300-500kbps, with some data sessions taking several seconds to connect." Once connected, they remained that way, but "it was like I was waiting in line to get on the Internet," Segan reported.

Last week, Sprint said it was "looking into a small number of reports of slow data speeds." But as PCMag's Segan pointed out, "we don't know how many of the people complaining about iPhone speeds on Sprint are experiencing Sprint's 3G network for the first time. As we showed in our 21-city Fastest Mobile Networks feature, Sprint has the slowest of the major 3G networks, with average national download speeds hovering around 480kbps compared to Verizon's 700kbps and AT&T's 2.4Mbps."

Prior to the iPhone 4S launch, meanwhile, Sprint Nextel CFO Joe Euteneuer told attendees at a banking conference that the carrier was preparing its network for the influx of usage should it get the iPhone. "We're going to stay ahead of it," he said of the demand.