Many modern blog platforms (most of them actually) let you publish data by email. You can just send an email to some service address and platform transforms it into a new post. For example, in Posterous you can send data to post@your_blog.posterours.com, in Friendfeed it was email@example.com, in Blogger you can set address in Settings->Email&Mobile tab, Facebook can update status by email too (see http://www.facebook.com/mobile/) etc.
Our updated Geo Post mashup helps you add location info to such emails. All you need is set an email address for update and get back a customized version of Mobile map mashup, that lets you send email updates to the provided address. Simply save short URL provided by GeoPost mashup in your mobile browser bookmarks or load it via generated QR code.
And just because Mobile map lets you share location info via SMS too (e.g. on Android platform), GeoPost lets you set also a predefined phone number for SMS. All in all – it is a configuration tool for Geo Messages.
P.S. mashup does not save your data on the external servers.