Apple watchers are getting plenty of signs the consumer electronics maker is adding LTE 4G connectivity to iPhones. But there are questions over when that might happen.

So far, we know code referencing LTE can be found in iOS 5 beta. Carriers are already testing LTE-enabled iPhones, and so is Apple, which is hiring LTE engineers and installed LTE network equipment in at least one of its stores.

First to fuel the speculation over a 4G LTE iPhone was BoyGeniusReport on Monday, reporting Apple’s carrier partners are testing iPhone models with LTE capability. Engadget followed up on Tuesday with a photo (that has now been removed) depicting 4G equipment recently installed at an unnamed major Apple store by AT&T, the report claimed.

Forbes joined the LTE iPhone party on Thursday, when it found job listings on LinkedIn that indicated Apple is seeking field test engineers with expertise in LTE, who will have to test the telephony (phone, sms, data, etc) functionality of the iPhone as part of the “iOS Quality team” of “QA” (Quality Assurance) engineers.

Saturday then brought a confirmation from MacRumors that code buried in iOS 5 beta (first indicated by BGR) was present in at least the last two developer builds of iOS 5, but only for some devices, namely GSM iPhone 4 and CDMA iPad 2. However, the report points to comments made by Apple’s Tim Cook, who said the first generation of LTE chipsets are forcing too many design compromises (such as battery life) for his company.

Despite suggestions from Forbes and 9To5Mac that LTE 4G iPhone testing could mean the iPhone 5 expected next month (and the iPad 3) would feature the technology, signs so far indicate that the iPhone 6 is the most likely to sport 4G. Electronista also points out the current need for an additional, separate 4G chip inside an iPhone, as chip makers prepare to merge 3G and 4G on one chip in 2012 -- just in time for the iPhone 6.

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