According to mobile phone networks in the UK, there is short supply of Apple's latest iPhone, which has left them "frustrated" and "concerned."
Several networks said that stock of the premium iPhone 5S was severely limited in the UK, and that would likely cause disappointment.
None of the networks wanted to be identified, however, over worries they could be further disadvantaged when supplies were replenished.
Despite lack of 5S devices, there is actually plentiful stock of the cheaper model, the 5C. Insiders from two of the companies told BBC news that they suspected Apple was trying to drive sales of the cheaper 5C model, but that their own figures suggested customers had been hesitant to place orders.
Apple has prevented networks and retailers from allowing customers to pre-order the 5S.
One network spokesman told the BBC they had "crates and crates" of the 5C, but that the higher-end 5S was being "drip fed" into the market, and networks and retailers had been left "in the dark" about Apple's schedule for replenishing the stock.
Less than one hour after going on sale in the UK, the 5S was listed on Apple's website as being unavailable for 7-10 business days for the UK.
O2 confirmed to the BBC that it would not be selling the 5S in its stores on launch day, but that customers would be able to try a"demo" model and place an order through their website.
It is the first time that O2 has had to put all of its stock online due to low availability, a spokesman confirmed.
Some Vodafone staff appeared confused about their company's position. One call centre worker told the BBC that there would be no 5S units in stores until Saturday. Another said that stock would be available on launch day in some of the network's stores, but that the firm did not yet know which.
A Vodafone spokesman later clarified, saying: "We will have models of both 5S and 5C in our stores across the country from tomorrow.
"We are doing as much as we can to ensure every store has every configuration. We will be very open with our customers about what we have available to them."
In Apple's flagship store on London's Regent Street, the BBC was told that details of stock levels had not been shared with staff due to "security reasons".
In the US, technology media have reported similar issues with supply. Technology news site AllThingsD.com quoted one US network as saying it had "grotesquely unavailable inventory" ahead of launch day.
Delays have become apparent in other markets as well. In Australia and China, customers buying the 5S directly through Apple have been told to expect to wait at least seven working days, while customers in Hong Kong and Singapore are being told the phone is not available until October.
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