Apple will hold a media event on Oct. 4 when the company will unveil its new, much-anticipated iPhone 5, according to reports. The release, likely adding Sprint as a sales partner, could deliver a crushing blow to the sinking BlackBerry and manufacturer Research in Motion (RIM).

Consider only the latest report from RIM, which said in a filing that its sales are plunging in the U.S. -- faster than many analysts expected. One reason is that once Verizon added the iPhone this year, Blackberry sales have dropped. BlackBerry sales also continue dropping at AT&T, the original iPhone distributor.

Once Apple's iPhone 5 is released to high demand, and if the company adds Sprint as a distributor, as expected, then RIM's BlackBerry to be dealt a fatal blow in the U.S.

Apple's iPhone unveiling is set for Oct. 4 and new company CEO Tim Cook will run the ceremonies, according to The Wall Street Journal blog AllThingsD. The new iPhone 5 is expected to be redesigned with a better camera and run on a dual-core processor. The report suggests the new iPhone 5 will go on sale within weeks of the unveiling event.

Meanwhile, in a filing Tuesday, RIM noted that the company already has a 50 percent year-over-year decline in U.S. revenue, largely because consumers are moving away from the BlackBerry to Apple's iPhone and Android-based smartphones.

RIM's customer concentration in the U.S. has also declined, and the company no longer has at least 10 percent of its revenue with either AT&T and Verizon Communications -- currently the two U.S. carriers of Apple's iPhone. Thus, for RIM, the situation looks bleak: wherever Apple's iPhone is sold, sales of its BlackBerry smartphones have declined the fastest.

Apple's iPhone, launched in 2007, is the bestselling smartphone in the world. Previously, RIM's BlackBerry was the top smartphone, before the iPhone came along, soaring to become the world's leading smartphone.

RIM, based in Canada, reported the information in a 6-K filing released Tuesday.

One analyst says RIM (NASDAQ: RIMM) faces long-term challenges, while another said Tuesday the company must release innovative products in time, while restoring investor confidence with credible earnings forecasts.

Citigroup's Jim Suva said in a note Tuesday that RIM's drop in revenue, which is spread across all regions but worse in the U.S., comes despite the fact that the August quarter the previous year was soft for RIM. Therefore, the suggestion is that RIM's year-over-year comparison shouldn't have been so weak.

But as AT&T and Verizon pushed iPhone and Android products in the past year, RIM has been unsuccessful at gaining meaningful share elsewhere, Suva said.

We see material challenges ahead for RIMM including a continuation of carrier promotion commotion that favors Android & Apple compared to a historical support for Blackberry, iPhone 5 launch that importantly should be a global phone for Verizon, developer confusion as to which Blackberry operating system to design for (BB6, BB7, QNX), and continued erosion of the company's enterprise business due to sandboxing and BYOD (Bring Your Own Device), Suva wrote in the investor note.