SamMobile, making it seem logical that the company would skip using the GT-i9400 as a model number.
So to recap, it seems that the Korean based manufacturer is testing software for two handset models, the GT-i9500 and the GT-i9505 (possibly an LTE enabled version of the phone). With a South Korean company expected to skip over the GT-i9400 because of the bad luck regarding the number "4", it could very well be two variants of the Samsung Galaxy S IV undergoing software tests. On the other hand, the GT-i9500 number is already being used on Samsung's TIZEN developer phone which would seem to give the edge to that platform being involved in the software tests. Additionally, earlier this year there was speculation that the first Samsung TIZEN handset would be released in February. Hopefully, we will have this all cleared up even before CES 2013 next month.
source: SamMobile via AndroidAuthority