vboxplay: 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/vboxplay - from package: isdn4k-utils

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

On Debian possible default full paths are:

/usr/bin/vboxplay - from package: isdnvboxclient

You may install the required package with command apt-get install {package}

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