The Korean firm rose to the top of the US charts for all mobile phone sales last May and has continued to strengthen its position ever since.
However, comScore claims that its market leading share has fallen by 0.3 percentage points in its latest report, which covers the three month period ending in March.
On the slide
Samsung presides over what is now a static market, with its nearest rival LG stagnant and some distance back on a 20.9 percent share.
Indeed, the only player currently enjoying any growth whatsoever is Apple, up 1.1 percentage points to a 7.9 percent share of the market.
On current projections, Apple should overtake rival RIM for fourth spot within the next couple of months, with BlackBerry continuing to fall back, down 0.1 percentage points since December.
Growing Google
Manufacturers might be suffering a stalemate, but from a smartphone platform perspective, it's still all about Android.
Google's OS has extended its lead over nearest rival BlackBerry according to comScore's March numbers. Android now holds almost 35 percent of all subscribers across the US, giving it a 7.6 percentage point lead over RIM's platform.
Apple is also growing its share, albeit at a somewhat slower rate. Latest figures suggest iPhone has a 25.5 percent share of subscribers, up 0.5 percentage points in the run up to March.
However, with BlackBerry dropping by 4.5 percentage points across the same period, it's likely Apple will move into second position within the coming weeks.
You can view a summary of the findings in full on comScore's website.
