Texting iPhone 3G

Where are you texting from and to? If you are in the US and texting to a different area code, you may have to put a 1 in front. Here, in Europe, I have a + in front of all the area codes, and need it to text messages outside Slovakia.
white macbook 1.83, 2 G RAM Mac OS X (10.5.4) kermit, the green iPod nano; iPhone 3G

You do not need to put in a 1 in front of the area code, that would make it an 11 digit. It is to a coworker who lives about 25 minutes from me. And its not only with him, its with others as well.

Im getting the same text back saying to enter the 10 digit number even though it is already. It is a local number. Anyone have any ideas to whats causing this.
Toshiba Windows Vista

I had this problem one, where I only entered the number with no area code and that it failed to send. I realized that I did not have the area code on that contact. Well I added the area code to that contact and sent the same message and still failed. I also checked the SMS side and still was sent to the same contact as before. So I deleted the SMS and resent it. and it worked for me.
So make sure on SMS you delete that sender first because it is still thinking it has the old contact, and resend it.
HP Pavilion DV2812tx Windows Vista iPod touch 16 GB, iPod Hi-Fi, iPhone 3G 16 GB (Black)

Its an old contact yes but the number never changed. When you put in the 10 digit number it brings up the persons name if they are in your address book. The only way that I have been able to avoid it is if I manually type the number in EACH time I send a text or go to the contact in the address book and hit text message. There needs to be some way that we are missing that allows the phone to keep the complete 10 digit number saved in the sms memory.