Sending a text message internationally works the same way as dialing a voice call. This website provides all the necessary information. Try a phone code search here. Alternatively, you can use the plus sign instead of your country's exit/IDD code. For example, in order to text from Europe to the US you can either use 00 1 or +1 followed by the 10 digit US cell number. In fact, some of our website's users have reported that texting internationally only works when using the plus sign.
There have been numerous reports of texting between countries not working, especially when trying to send a message between the USA and Europe. Generally, the reason for this is an incompatibility between the two wireless carriers. Namely, most wireless carriers in Europe and around the world use GSM technology while the big carriers in North America use CDMA. Messaging platforms are different for GSM and CDMA and, although texting is commonly used and working between the two types of networks, often cellular subscribers encounter problems texting internationally. If you followed the instructions on this website and your text message didn't go through call your wireless carrier to inquire about this issue.