We have found one software suitable in our database for this conversion.
It looks like that even the latest version of Microsoft Video Maker supports the previously used MSWMM format and thus users should be able to open and import these files and access the project.
This can be typically done using he "File ► Save movie" function is then possible to export the projects as 3GP multimedia file, which is what mswmm to 3gp conversion or export essentially is.
MSWMM
Files with mswmm extension can be most often found as projects from Microsoft Windows Movie Maker, a video creating/editing software application, included in Microsoft Windows Me, XP, and Vista.
3GP
Files with 3gp extension are multimedia files in format designed originally for 3GPP networks based on MPEG-4 standard.