Q. One of my sons has been charged by T-Mobile for more than 300 outgoing international text messages from his iPhone 4 that he adamantly says he didn’t send. All $64.40 worth of text messages were to numbers in England, and all to 10 similar phone numbers (differing only in the last two digits.) They start with 447537410207.

T-Mobile representatives kept insisting that my son sent the text messages, and I finally agreed to pay an extra $10 a month charge for my son to have unlimited international texting. In return for that, T-Mobile representatives agreed to erase the charges for the texts to England. That gave us some breathing room to try to determine how these international texts were sent and billed to my son’s account.

My son had been using iMessage, Apple’s instant message service, but he quit using it a week or so ago. What happened?

Bill Jafvert New Brighton, Minn.

Your son is right, he didn’t send the text messages to England. His iPhone did.

All the phone numbers for which you received international charges belong to Apple. Your son’s iPhone sent a text message to Apple Internet servers based in the United Kingdom every time he activated the phone’s iMessage feature. Activating the Facetime videoconferencing feature would have had the same result.

This is a problem that only happens on the T-Mobile cellular network because T-Mobile has limited compatibility with the iPhone 4. T-Mobile doesn’t sell the iPhone 4, but allows the phone to be used on its network.

This limits the iPhone’s Internet speed on T-Mobile’s network, and can result in unexpected billing for international text messages. The latter problem hasn’t been well-explained to users, and iPhone message boards include many complaints about it.

What can you do?

By adding international texting to your T-Mobile plan for an extra $10 a month, you’ve solved the problem. Another solution, which wouldn’t be appealing to your son, is to turn off iMessage permanently.

T-Mobile said it is researching the problem and will contact you.Q. For years I used AppleWorks software, but now that I’ve upgraded to Mac OS X 10.8 (also known as Mountain Lion), I can’t open any of my AppleWorks files. What can I do?

Judy Warren Lakeland, Fla.

AppleWorks, which has been discontinued by Apple, is not compatible with the Mountain Lion operating system. Try Apple’s iWork software, which is supposed to be able to open AppleWorks word processing, spreadsheet and some other documents.