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Mobile commerce has hit a milestone: Today there are more than 100 m-commerce sites and mobile applications that enable consumers to shop and make purchases on their mobile phones.

97 merchants operate 103 transactional mobile sites and apps. Apple Inc., No. 5 in the Internet Retailer Top 500 Guide, operates two apps; Foot Locker Inc., No. 53, runs five sites; and Polo Ralph Lauren, No. 88, operates two sites.

In addition to the 103 transactional m-commerce sites and apps, seven more e-retailers operate seven additional mobile web sites or apps that do not enable purchases but instead focus on browsing product catalogs or reading customer reviews.

Among merchants in the Internet Retailer Top 500 Guide, 41 run 47 sites and apps. There are 29 m-commerce apps today; some e-retailers operate both a site and an app, or, in the case of Apple, two apps.

“M-commerce is likely to follow the history of exponential growth previously experienced by the e-commerce surge,” says Adam Boysen, a project manager who follows m-commerce at e-commerce and m-commerce consulting firm Acquity Group LLC. “Given the significant amount of growth in the mobile channel that we’ve seen this year, I believe the tipping point for online retailers to start developing a mobile strategy has already passed. The larger online retailers that have invested in the mobile channel are poised to benefit the most from marketing their mobile presence to early adopters, and from the exponential revenue growth rates that will soon follow.”

Retailers in m-commerce today run the gamut from tiny web-only merchants to giant mass merchants and department stores. Heavy hitters with m-commerce sites and/or apps include: Amazon.com Inc., No. 1 in theInternet Retailer Top 500 Guide; Sears Holdings. Corp., No. 7; Overstock.com Inc., No. 29; 1-800-Flowers.com Inc., No. 31; and Foot Locker.

Showing that any retailer can run a mobile sales channel, many small e-retailers are blazing the trail. These include BuyCD.com, Café Britt, Comedy Central and Online Scuba.

The vast majority of retailers in m-commerce employ technology vendors to build and help maintain their mobile sites and apps. The movers and shakers among mobile technology vendors building m-commerce sites and apps are CardinalCommerce Corp., Digby, Moonshadow eCommerce Inc., mPoria Inc., Unbound Commerce and Usablenet Inc.

Last week, in talks with Internet Retailer, leading m-commerce technology vendors revealed they’re having a rush of retailers wanting to get a mobile presence up and running before the holidays, and that within the next three months they expect to launch a combined total of about 20 new m-commerce sites and apps.