Alphanumeric means characters that are only letters A-Z (upper or lower case) and numbers 0-9. If you have ever created a username or password that rejected symbols like ! or @, you were being limited to alphanumeric characters.
What is alphanumeric
Alphanumeric is a term that describes a character set consisting solely of the letters A through Z and the digits 0 through 9. Common examples include password requirements that specify "letters and numbers only" or username fields that do not accept special characters.
What alphanumeric does not include
Alphanumeric does not include special symbols such as !, @, #, $, %, &, or *, and it also excludes punctuation marks like periods, commas, and question marks. Spaces are not alphanumeric either. A common misconception is that symbols count as alphanumeric, but in strict technical definitions and SMS sender ID rules, they do not.
Where you encounter alphanumeric characters
You encounter alphanumeric characters every day when creating passwords, filling out online forms, entering data into spreadsheets, and working with computer programming. Many websites enforce alphanumeric-only fields for usernames to avoid confusion with special characters. In programming, variable names and function names are often restricted to alphanumeric characters plus underscores.
Alphanumeric sender IDs for SMS
In SMS messaging, an alphanumeric sender ID is a brand name made from letters and digits that appears as the sender instead of a phone number. Most services limit these IDs to 11 characters and require at least one letter. Spaces may be allowed by some carriers, but punctuation and symbols are not. The exact meaning and limits depend on the service or carrier, and the documented ranges vary by country and network. SMSGlobal requires no full stops or spaces in alphanumeric sender IDs, and the ID must be no longer than 16 digits or 11 alphanumeric characters. Telnyx says an alphanumeric sender ID must be between 3 and 11 characters, can include spaces, and cannot be only numbers. Bandwidth says standard alphanumeric sender IDs may include space.
Country and carrier restrictions
Alphanumeric sender IDs are not supported by carriers in the United States or Canada. In many other countries, carriers may reject alphanumeric sender IDs entirely, and some countries require pre-registration before you can use one. Rules vary significantly by network, so checking local regulations is necessary before sending messages with an alphanumeric sender ID.
How to register an alphanumeric sender ID
Registration steps differ by provider. Using Bandwidth as a concrete example: log in to the Bandwidth App, click Support, select Ask a question, ask to register a Sender ID, then click Create ticket and submit the form with the required business documentation. For other providers, such as Telnyx, the sender ID is set dynamically in the FROM field of the SMS API request. Some carriers require carrier-side registration, and country rules determine whether registration is needed. SMSGlobal's help page does not give a step-by-step menu path for changing the sender ID; it only states the format rules and that some carriers may reject alphanumeric or numeric sender IDs. If you need help with phone numbers and calling help, the Bandwidth support portal covers both Phone Numbers, Calling and Messaging Help.
Frequently Asked Questions
Can I use numbers only for an alphanumeric sender ID?
No. Most services require at least one letter in an alphanumeric sender ID. A numeric-only sender ID is treated differently and may not be allowed under alphanumeric rules.
What is the maximum length for an alphanumeric sender ID?
The documented limit is 11 characters on most major platforms, though SMSGlobal also states "16 digits or 11 alphanumeric characters." Always check your specific carrier's limit.
Do all countries accept alphanumeric sender IDs?
No. The United States and Canada do not support them, and many other countries have restrictions or require pre-registration. Carrier support varies by network.
Can I use lowercase letters in an alphanumeric sender ID?
Yes. Most services accept both upper- and lowercase ASCII letters, though some carriers may convert the case or reject non-standard formatting.
Is an alphanumeric sender ID the same as a short code?
No. A short code is a 5- or 6-digit number used for SMS, while an alphanumeric sender ID is a text-based name. They follow different registration rules and have different carrier requirements.
