ComScore issued its January snapshot of the U.S. mobile phone market Tuesday — with accompanying pie chart here — but if you want to understand what the numbers mean you should check out Horace Dediu’s Wednesday morning report on Asymco.com.

Dediu seems to be the only analyst who tracks these monthly reports over time. Graphing two years of comScore data in various clever ways, some clear trends emerge:

• By the fourth quarter of 2012, the U.S. carriers will be adding new smartphone subscribers at the rate of 1 million every week
• 35 million U.S. users switched to smartphones in 2011. Dediu now forecasts that smartphone penetration will reach 50% of the user base by June 28.
• Apple (AAPL) and Google (GOOG) have continued to gain market share while Research in Motion’s (RIMM) BlackBerry and Microsoft (MSFT) continue to lose.

RIM and Microsoft are quickly running out of options. As Dediu puts it:

The “comeback story” for any of the hopefuls will depend either on switching users away from their current platforms or trying to engage with late adopters. The first option is daunting due to latent network effects related to platforms and the second sounds to be symmetric to existing incumbent strategies.

Without an asymmetric approach, the challengers are unlikely to succeed.

In other words, unless RIM and Microsoft come up with something totally disruptive, they’re going down.

For the rest of Dediu’s comScore charts, see The unrelenting trends in the US smartphone market.