Apple stock closes at an all-time high of $429.11

Apple (s aapl) had a record-breaking day in trading Wednesday, closing at an all-time high of $429.11 per share, after peaking earlier in the day at $429.47. Its market cap rose to just shy of $400 billion, sitting at $398.82 billion as of this writing.

Stock prices may have been buoyed by news that Apple continues to regain mobile market share based on the strength of its iPhone 4S sales. Nielsen (s nlsn) reported Wednesday morning that since the introduction of the 4S, Apple’s share of the smartphone market has climbed steadily in the U.S. The Nielsen report’s findings are very similar to U.S. smartphone numbers released by NPD last week.

Apple also has an earnings call scheduled for Jan. 24, at which many analysts expect the company to announce record sales across its device lineups. We’ll likely see some numbers revealed early at tomorrow’s special education event in NYC on Thursday, since Apple typically spends some time at media presentations talking up recent successes and revealing information like up-to-date App Store download numbers, for example. We’ll have live coverage of that event beginning at 10 a.m. EST.