Timeout issue when sending SMS via AT+CMGS

[KCH390]

When I try to send text messages via "atcom AT+CMGS="my_phone_number", "CR", "Text message text", I always get a timeout error. I'm able to send other AT commands without issue. I think the problem has to do with how atcom terminates the message stream, but I'm not certain what I need to change to fix this. Any help would be greatly appreciated!