Apple’s iPhone strategy was dealt a fresh blow today when its exclusive partner in Germany — Europe’s largest market — was forced to make the gadget available on rival networks.

T-Mobile said that it would, with immediate effect, make the phone accessible to other mobile operators.

The move followed a legal challenge by Vodafone which claimed that the exclusive deal — under which customers were forced to sign up to a 24-month T-Mobile contract — breached local competition laws.

The decision by the German operator to cave in to opposition from its rivals marks the latest in a series of blows for Apple and its iPhone strategy.

In an attempt to maximise revenues from the gadget — a combined iPod music player, internet surfer and mobile phone — the Californian group negotiated exclusive market by market deals across Europe.

In return for exclusivity the chosen mobile operator had to hand over up to 30 per cent of continuing subscriber revenues to Apple.

It is unclear how that model can proceed in Germany now the phone has been opened up for use on other networks.

The model has also been blown apart in France, where local laws have forced Orange — Apple’s chosen network partner there — to open up the phone to rival networks when it goes on sale at the end of the month.

The UK is now the only European market where the deal remains exclusive to one partner, O2.

In an effort to limit damage, T-Mobile, which launched the phone on November 9, said that it would charge €999 (£720) for an iPhone without a contract.

With a T-Mobile contract, the gadget costs €399.

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