I'm currently using a Cisco 881G2 Router which has a Cellular interface.
Sending Text messages from the router is as simple as typing the following command:
cellular 0 gsm sms send <telephonenumber> <message>
Sending messages containing plain text works just fine.
According to the GSM 03.38 standard, there are 128 characters in the Basic Character Set. Several of these chracters however, require the use of an 8-bit ASCII character set, which is not the default in Cisco IOS. Thanks to Brett Lykins' answer below, I have been able to configure my router to accept 8 bit ASCII characters, including some of the Scandinavian characters like æ, ø, å and the capitilized versions of these. Using Telnet doesn't give me the option to send special characters, but both Putty and SecureCRT over ssh does allow me to send these special characters.
Regretfully, even after making these very helpful modifications, the text messages being do not arrive correctly. The two tests I did are:
cellular 0 gsm sms send 00474792xxxx Hålla! cellular 0 gsm sms send 00474792xxxx Greetings æ, ø, å
My mobile phone received the messages "Hemla!" and "Greetings f- x- e", rather than what was sent. I have for security reasons obfuscated my mobile number above.
The question is - how does one send a text message which contains these types of characters?
Unfortunately, the Configuration Guide provides no clues on how to do this.
The router runs C880 Software (C880DATA-UNIVERSALK9-M), Version 15.2(3)T2 I have tried with Putty, and with SecureCRT 7.0.3 on Windows using VT100 emulation.