Who I have the same questioned this topic

I've only had the phone for about 10 months, and yesterday I accidentally left it at home while I was at work. When I got home, I noticed that I couldn't send any text messages until I was within range of our house wifi network. Since I was home for the night, I didn't notice anything else, it was working fine. Then, this morning, I tried going on twitter, checking my email, making a phone call, and sending texts while I was on the train. I couldn't do any of them. Nothing worked. At work, connected to wifi again, it's fine. So anyone have any idea what's going on here?