You can safely send ASCII information over SMS, provided you are encoding your characters to Binary PDU first.
Some of the newer GSM modems like Wavecom and Multitech would even allow direct ASCII or even Unicode data to be sent.
To check whether your modem supports SMS Text mode (instead of Binary PDU mode) use the following command
AT+CMGF=1
If the response is "OK" this is supported. That means you can send ASCII character set messages (No Unicode though)