Everyone’s got their own pet theory on when and if a 3G version of the iPhone is going to be made available. But this week, one of the many Apple iPhone hackers out there claims to have found the most solid evidence yet that a 3G version of the device is imminent.

Zibri, the hacker behind the ZiPhone application, one of the original jailbreaking and unlocking tools for the iPhone, made the discovery while trawling through the code for the iPhone beta SDK.

In the code there is a line which makes reference to the Infineon SGOLD3H chipset, otherwise known as the PMB8878. The currently available iPhone uses the SGOLD-28876 as its EDGE-capable baseband processor. The SGOLD3 however is fully HSDPA 7.2Mbps capable, which suggests the next generation iPhone will pack blazing fast connectivity.

More suggestive evidence of the existence of a 3G iPhone also turned up late last month when Japan’s biggest intercom maker, Aiphone, revealed that it has been in discussions with Apple since last summer and has recently come to a friendly agreement that will allow the Californian gadget vendor to use its beloved “iPhone” brand in Japan.

It turns out Aiphone owns the trademark to the “Aiphone” brand in Japan and about 70 other countries. But while “Aiphone” and “iPhone” are spelt differently in English, the phonetic similarities apparently give Aiphone the company the rights to the “iPhone” trademark in Japan.

Regardless, it’s probably a safe assumption that Apple wouldn’t go to all this trouble if it wasn’t going to launch the iPhone in Japan, which has a technological landscape that lends itself to 3G – NTT DoCoMo and Softbank on WCDMA and KDDI on 1x EV-DO.

Aside from this, the apparent drying up of iPhone supplies in the US has set tongues wagging, as has T-Mobile Germany’s latest move to cut iPhone prices as part of a strategy to shift units. Personally, I think it’s a sure thing that a 3G iPhone is in the pipeline, and it looks like the Apple Developers Conference in June is the safest bet for an announcement. After all the final version of the 2.0 software is already penned in for release at that event, so why not have new hardware to go with it.