Well I don't think you are being completely fair. They aren't saying they don't want to fix the problem, but without seeing the issue how will they know what to replace, repair or fix? Intermittent issues are as much a struggle for the company repairing them as the customer, they require a lot of time, and expense to resolve. If they "guess" and you get it back and it's still faulty, you are likely to be mad as hell they didn't fix it "properly" and may well post in some forum about how crappy the service is from xxx repairer.
Indeed but Im not disputing the repairer wants to sort the problem, I'm sure they do. My issue is the customer has a right after purchase for the goods to be either serviced so the fault is no longer or the item replaced.
They can keep and use the phone for a resonable period to observe the issues but returning it to the customer with 'no fault found' is not acceptable.