sms2xml: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/sms2xml - from package: smstools

You may install the required package with command yum install {package}

Error in other languages:
sms2xml: bevel nie gevind nie
sms2xml: comandă negăsită
sms2xml: comando não encontrado
sms2xml: commande introuvable
sms2xml: command not found
sms2xml: käsku ei ole
sms2xml: không tìm thấy lệnh
sms2xml: komanda nerasta
sms2xml: Kommando nicht gefunden.
sms2xml: kommandot finns inte
sms2xml: komut yok
sms2xml: nie znaleziono polecenia
sms2xml: níor aimsíodh an t-ordú
sms2xml: no se encontró la orden
sms2xml: no s'ha trobat l'ordre
sms2xml: opdracht niet gevonden
sms2xml: parancs nem található
sms2xml: perintah tidak ditemukan
sms2xml: príkaz nenájdený
sms2xml: příkaz nenalezen
sms2xml: команда не найдена
sms2xml: командата не е открита
sms2xml: 命令找不到
sms2xml: コマンドが見つかりません