Your old iPhone will be upgraded, too. If you have the original iPhone and are feeling a bit envious, be aware that it will get a software upgrade, too, also available on Friday. (It's free for iPhone owners and $10 for owners of the iPod Touch, the iPhone-minus-the-phone device that launched last September.) You won't get GPS or 3G network access, but the upgrade will provide old iPhone owners with better e-mail management, more sophisticated contact searches, and support for heavy-duty Office applications such as PowerPoint. And both iPod Touch and iPhone owners will have access to a whole slew of applications from third-party developers (typically $10) covering gaming, chatting, social networking, traveling, news, sports, finance, or business. So you might consider adding a web app like FastPriceCheck, an application that  finds product details, user reviews, and compare the lowest online prices using any product's barcode.

History suggests supplies will be plentiful. Rumors of short supplies compelled many customers to line up in front of Apple and AT&T stores during last year's iPhone debut. But there were plenty of $499 iPhones available then. While it's hard to predict exactly how supply and demand may align this time, especially given the much lower price, we'd err on the side of assuming the new iPhone will be widely available for some time and avoids the crowds on Friday. Another reason to avoid the initial rush: The 3G will have to be activated in stores, which could make lines move more slowly than with the original, which you activated at home.

Tests may turn up glitches. A new product, even one with a promising pedigree like the iPhone, may have glitches or quirks that might affect your buying decision. Wait for the assessment of experts, which will likely begin on Wednesday and Thursday with previews from the select few reviewers whom Apple bestows with advance units. Since we buy every product we test, we'll be joining the fray to buy our new iPhones at stores on Friday morning. We plan to begin posting our first impressions on Friday or Saturday. By then, a myriad of new owners will also have weighed in via the likes of this blog, Engadget and Gizmodo.

Plan costs. As we've reported previously, the relatively affordable (for a smartphone, anyway) price tag for iPhone 3G is accompanied by a minimum cost of $70 for a voice/data plan. That compares with the $60 minimum with the old iPhone. And even that $60 plan came with 200 text messages a month thrown in; with the 3G, you need to pay $5 a month on top of the $70-plus plan for 200 messages—or pay a hefty 20 cents per message a la carte.

—David Toner and Mike Gikas