When mobile payments finally make their debut on the iPhone, no one will be surprised.

Apple (AAPL) has been notoriously slow at venturing into transactions. The latest iteration of its mobile operating system, iOS6, is a testament to the crawl.

This past fall, iPhone users who updated their devices got a look at Apple's de facto mobile wallet, Passbook, which now holds multiple loyalty cards and coupons and tickets that are redeemable at the counter with a barcode displayed on the device's screen.

And more recently, Apple included a voice recognition feature (using Siri) that lets people purchase theater tickets through the movie app Fandango by speaking.

Both features were already being tested by developers working on Apple's open API, placing apps into iTunes that mimicked some of the developments that the tech giant eventually marked for broader release.

"It's all proven, there is no real inventing left, because it all works as is, it's all tweaks from here on," says Matthew Harris, managing director, Bain Capital Ventures.

For instance, Chirpify chief executive Chris Teso says he began using Siri to make purchases in his company's tweet-to-pay service long before Apple made its last iOS6 change.

"Siri is just another way to facilitate a tweet, Instagram or Facebook comment, so Siri + Chirpify = payments now," he says, over Twitter. "Since Siri is just speech to text, users could tweet 'buy' to items for sale."

Indeed, there is widespread belief that it's only a matter of time before Apple adopts mobile commerce.

Asked if she thinks Apple sees and learns from work-arounds like the one Teso is using, CEB Towergroup research director Nicole Sturgill says, "Absolutely. That's why they can afford to take their time on their own initiatives," she says, also over Twitter. "I also think it's true that mobile payments will really hit mainstream when the iPhone is fully enabled."

Harris explains that while third-party programmers have already proven that mobile payments are possible on Apple devices, that sends mixed signals to onlookers because none of these solutions seem to have the juice for widespread adoption.

A possible reason for Apple's snail-like pace in payments? Apple wants to make sure whatever move it makes is an instant hit, because of its scale.

After all, there are few companies with Apple's market-moving user base — you can count Facebook (FB) and Walmart (WMT) among them — that have the ability move the mobile payments dial as quickly or drastically as it can.