Mobile phone spam is a form of spam (unsolicited messages, especially advertising), directed at the text messaging or other communications services of mobile phones or smartphones. As the popularity of mobile phones surged in the early 2000s, frequent users of text messaging began to see an increase in the number of unsolicited (and generally unwanted) commercial advertisements being sent to their telephones through text messaging. This can be particularly annoying for the recipient because, unlike in email, some recipients may be charged a fee for every message received, including spam. Mobile phone spam is generally less pervasive than email spam, where in 2010 around 90% of email is spam. The amount of mobile spam varies widely from region to region. In North America, mobile spam steadily increased after 2008 and accounted for half of all mobile phone traffic by 2019. In parts of Asia up to 30% of messages were spam in 2012.

The lesser and geographically uneven prevalence of mobile phone spam is attributable to geographic variation of prevalence of mobile vs non-mobile electronic communications, the higher cost (to spammers) of and technological barriers to sending mobile messages in some areas, and to law enforcement in others. Today, particularly in North America, most mobile phone spam is sent from mobile devices that have prepaid unlimited messaging rate plans. While the rate plans allow for unlimited messaging, in reality the relatively slow sending rate (on the order of magnitude of 1/s) limits the number of messages that may be sent before an abusing mobile is shut down.