In January, I suspect we will all be tightening our belts after some serious spending over Christmas. Unfortunately, if you are an Orange customer, that's going to be a little less easy.The company has confirmed a price rise for all pay monthly customers, working out at 4.34% across the board. So if you are paying (for example) £35 per month, you'll now get a bill each month for £36.50. Ok, it doesn't sound a lot, but if you are short of cash, that is money you would rather not give out, especially if you have signed a contract agreeing a different amount. If you want to know exactly how much your rise will be, there's a handy calculator on the Orange site showing you.Why the rise? Inflation, according to Orange: 'As you probably know, inflation is at a 20-year high, which is having a significant impact on businesses and households alike. Unfortunately, we've had to re-evaluate our prices for the first time and are sorry to say that there will be a 4.34% increase in our monthly plan prices from 8 January 2012.'Fancy leaving your deal because of it? That doesn't seem possible, with Orange doing everything by the book. In a post on Twitter, the company said: 'Our pay monthly terms and conditions allow us to increase charges by up to the RPI figure in any 12 month period.' The company has also given the one month's notice required to push through the price rise. As we said, everything by the book.But all might not be lost. Martin Lewis from MoneySavingExpert.com said: 'This isn't a clear-cut case – so predicting the outcome of any complaint is tough. However, for those who want to escape their contract, it is worth formally contacting Orange and telling it you believe the price hike is of 'material detriment' and you want to leave. There is a slight chance the company will prefer to let some people go on an ad hoc, goodwill basis rather than risk having lots of people complain to Ofcom.'There are no reports of other networks following suit, but if Orange gets this through, you wouldn't be surprised to see others pushing up prices too. More on that if or when we hear anything.