T-Mobile has started to offer iPhone 3G models to UK subscribers, but only those currently spending big with the network and threatening to leave.

According to reports iPhones will be offered to a very limited number of T-Mobile customers every week in an attempt to get them to stay with the firm if they are thinking of moving to a rival network. Reports suggest that just 150 iPhones will be offered per week.

Customers have to be spending at lease £75 a month on the T-Mobile contract at the moment to be offered the iPhone 3G, which is the original Apple mobile phone.

The gadget giant released a new version, called the iPhone 3G S, earlier this summer, which remains available only via O2.

Customers will be offered an unlocked 3G so it appears that the deal is not breaking O2’s exclusivity deal, due to expire at the end of this year. Reports emerged last month that Apple was in talks with both T-Mobile and Orange about selling the iPhone 3G once the O2 deal runs out.

T-Mobile has been struggling in the UK market recently and in June it was reported that rival Vodafone was preparing a takeover bid for the beleaguered firm. T-Mobile is owned by German firm Deutsche Telekom and reports suggest it is keen to get out of the crowded UK mobile phone market, which is one of the most competitive in Europe. T-Mobile currently enjoys a 15% share of the UK market, with Vodafone on 25%.