My question:  I don't think I did anything originally, but my I-phone was all of a sudden not syncing with my calendar.  This morning I opened the "mobile me sync preferences" and checked the "synchronize with mobile me" box and put it on "Automatic". Then I checked the calendar box and the mail box, and it synced my calendar, but ever since, my phone says it has "no service" and will not allow me to call out or receive calls.   But it is getting e-mails........and my calendar.  What have I done and how can I correct this??

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Sounds like your phone has lost the signal to the ATT cell tower near by but is still on your wireless network. This would explain why data continues to go through but no calls are happening. Calls rely on the cell tower down the street. Data like email and calendar syncing can rely on the wireless network as well as the cell tower.

I would suggest you reset your phone by holding down both buttons on your phone for a few seconds until you see the red slider. Then turn the phone back on to see if it rediscovers the cell tower.

It could also be explained by something having happened to your sim card inside the phone. You may want to take it by ATT or Apple store and have them change the card out. ATT may be the best bet on that one. I don’t think the Apple store deals with the sim cards.

Last explanation...you could have been late on your phone bill and ATT turned off service!