As Nokia continues to give up market share, Samsung and Apple are persisting in their tug-of-war to lay claim as the world's top smartphone vendor. And while Nokia's smartphone shipments have nosedived year-over-year for the first quarter, lagging overall sales have made Samsung the number one mobile vendor worldwide.

The overall mobile phone market declined slightly for the first quarter, with shipments down 1.5 percent according to market research firm IDC. Nokia, which had been the number one mobile phone vendor since IDC began tracking the market in 2004, has continued its slide in market share. With overall shipments down 23.8 percent year-over-year, it has now dropped to number two—still holding a respectable 20.8 percent market share.

Unfortunately for Nokia, the competition isn't letting up. Samsung posted a 35.4 percent year-over-year increase in units to take the top spot among all mobile phone vendors. It now holds a commanding lead over Nokia, with a 23.5 percent share. Apple, which became number three in mobile phone sales last quarter after its blowout launch of the iPhone 4S, held its spot. The company still managed to increase shipments 88.7 percent year over year, enough to grab almost 9 percent of the mobile phone market with just its iPhone alone.

China-based ZTE grabbed a point of extra share for the quarter, up to 4.8 percent for fourth place. However, LG's shipments slid significantly, dropping down to fifth place with just 3.4 percent. A wide variety of manufacturers battle for the remaining 39 percent of the mobile market.

Smartphones are still where the real money is, though—overall shipments are up nearly 43 percent year-over-year—and that is catapulting Samsung and Apple to the top of the mobile market.

"The halcyon days of rapid growth in the smartphone market have been good to Samsung," Kevin Restivo, senior research analyst with IDC, said in a statement. The company had an outstanding 267 percent growth in unit shipments year-over-year, according to IDC's reckoning, making it the top smartphone vendor for the quarter with 29.1 percent market share.

Though Samsung no longer reports smartphone or tablet sales numbers publicly for "competitive reasons," IDC's estimates jibe with estimates from Juniper Research (which also ranked Samsung on top for the first quarter). Both companies disagree about just how well Samsung did compared to Apple, however—IDC gives Samsung a 7 million unit lead, while Juniper gives it a dominating 12 million unit advantage.

Still, nearly 60 percent of smartphone shipments in the first quarter were from either Samsung or Apple. Apple's shipments were up significantly for the quarter, as we noted previously, enough to gain several points of share to nearly 25 percent, according to IDC data. Apple benefited from a major launch of the iPhone 4S in China, as well as sustained demand globally. And its gross margins continue to earn it more revenue than Samsung, despite the differences in unit shipments.

"Apple's revenues from [iOS sales] continue to remain significantly higher than Samsung's, even when you take into account the latter's feature phones," Juniper Research analyst Daniel Ashdown said in an e-mailed statement. Apple's iPhone revenue alone was $22.7 billion for the quarter, while Samsung’s entire mobile division booked about $17.0 billion.

Apple and Samsung have swapped the top two spots for the last four quarters, but their rivals have struggled to hang on to diminishing market share. No one felt the sting more seriously than Nokia, which is still bearing the brunt of its switch to Windows Phone. Its smartphone shipments were down over 50 percent year-over-year, enough to drop from 23.8 percent share last year to just 8.2 percent.

RIM and HTC haven't fared any better, either. RIM is still struggling to ship its next-generation BB10 operating system, which it showed off publicly for the first time on Tuesday. It holds on to fourth place, with share dropping seven points to 6.7 percent. HTC lost half its market share as well, holding fifth place at 4.8 percent, though it seems to be banking on its recent One X and One S models to turn its tides.

"With other companies in the midst of major strategic transitions, the contest between Apple and Samsung will bear close observation as hotly anticipated new models are launched," senior IDC analyst Ramon Llamas said.