sms2html: 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/sms2html - from package: smstools

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

Error in other languages:
sms2html: bevel nie gevind nie
sms2html: comandă negăsită
sms2html: comando não encontrado
sms2html: commande introuvable
sms2html: command not found
sms2html: käsku ei ole
sms2html: không tìm thấy lệnh
sms2html: komanda nerasta
sms2html: Kommando nicht gefunden.
sms2html: kommandot finns inte
sms2html: komut yok
sms2html: nie znaleziono polecenia
sms2html: níor aimsíodh an t-ordú
sms2html: no se encontró la orden
sms2html: no s'ha trobat l'ordre
sms2html: opdracht niet gevonden
sms2html: parancs nem található
sms2html: perintah tidak ditemukan
sms2html: príkaz nenájdený
sms2html: příkaz nenalezen
sms2html: команда не найдена
sms2html: командата не е открита
sms2html: 命令找不到
sms2html: コマンドが見つかりません