Show all versions of multiline text field (Appended text)

1. Open site with SharePoint Designer and Insert a DataView WebPart(DVWP) on a page including your multiline field.
2. Switch to codeview and find the line that reference the field. (need to replace - <xsl:value-of select="@Comments" disable-output-escaping="yes" />

3. Replace with:
<SharePoint:AppendOnlyHistory runat="server" FieldName="Comments" ControlMode="Display" ItemId="{@ID}"/>

You will see the all the comments with author and dates.

To get all the versions for Multiline text field

allComments = "";

foreach (SPListItemVersion versionListItem in item.Versions)

{

        if (versionListItem["Comments"] != null){

               allComments += versionListItem["Comments"].ToString();

        }

}