I searched but didn't any info on this or find anything in the manual. What format is OK for phone number on a Sprint device?

For example on my GSM phones, all the number are in the format "+(country code) (area code) number". An example would be +1 (800) 555-1212. When putting my contacts in a Sprint Treo 650, it seems like it can dial these numbers fine (at least for those I've tried). However, I tried to send an SMS to my GSM number using this format and it seemed to go but the message never showed up. If I edited the number to remove the +1 (so it was now something like (800) 555-1212) it worked immediately.

How are numbers supposed to be formatted? How would you send a call or message to an international number?