UPDATE: The numbers in this report have changed, thanks to reader Dennis Forbes, who got his hands on the original survey results. See here.

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More than two thirds of smartphone owners surveyed by a German marketing firm say they may switch to another operating system when they buy their next phone.

The smartphone that elicited the most loyalty was the iPhone, with 59% of respondents saying they were sticking with Apple’s (AAPL) iOS. That’s considerably lower than the 73% in another survey who said they were “very satisfied” with their iPhone.

“Loyalty with a handset is a lot more complicated these days in that people buy into experiences at the high-end level,” Ryan Garner, an analyst with GfK, told Reuters.

“If a phone doesn’t do what it says it will do or what the owner hopes it will do, the maker will lose loyalty.”

Owners of smartphones running Nokia’s (NOK) Symbian software were the least loyal in GfK’s survey, with only 24% planning to stick with their operating system, followed by Microsoft (MSFT) Windows Mobile at 29%, Research in Motion’s (RIMM) BlackBerry at 35% and Google’s (GOOG) Android at 44%.

A significant number of Windows Mobile and Android users said they were going to stick with their smartphone OS, but were planning to switch handset models.

The survey was conducted in October and November among 2,653 mobile phone users in Brazil, Germany, Spain, Britain, the U.S. and China.

GfK also found that 37% of ordinary cellphone owners surveyed planned to upgrade to a smartphone when they bought their next phone.

[Follow Philip Elmer-DeWitt on Twitter @philiped]