internal/Resolve-NetBiosName.ps1

function Resolve-NetBiosName {
    <#
.SYNOPSIS
Internal function. Takes a best guess at the NetBIOS name of a server.
 #>

    [CmdletBinding()]
    param (
        [Parameter(Mandatory = $true)]
        [Alias("ServerInstance", "SqlServer")]
        [object]$SqlInstance,
        [PSCredential]$SqlCredential
    )

    $server = Connect-SqlInstance -SqlInstance $SqlInstance -SqlCredential $SqlCredential
    $servernetbios = $server.ComputerNamePhysicalNetBIOS

    if ($null -eq $servernetbios) {
        $servernetbios = ($server.name).Split("\")[0]
        $servernetbios = $servernetbios.Split(",")[0]
    }

    return $($servernetbios.ToLower())
}