Caldwell was last week named in the IRFU PricewaterhouseCoopers High Performance Select Group and played in the Churchill Cup for Ireland 'A' last summer.
Williams is currently typing up some loose ends in Australia but is in daily contact with the Ulster squad and management. He said: "This is a great boost for Ulster Rugby. Ryan has been earmarked for great things since he was a schoolboy and has progressed through the age-grade set-ups to a regular place with Ulster and recognition at Ireland 'A' level.
"His inclusion in the High Performance Select Group will provide him with further opportunities to improve his skills, and be involved with the national squad and I've no doubt that he will be part of Eddie O'Sullivan's vision going forward."
A former Ulster Schools Cup winning captain with RBAI, Caldwell joined the Ulster set-up on a development contract in 2003 while still eligible for the Ireland Under-21s and he participated in two junior (U-21) World Championships, in Scotland in 2004 and in Argentina in 2005.
Following his performances in the green jersey at U-21 level, he made his Ulster debut in October 2005 against Treviso in the Heineken Cup and this season has become a regular member of the Ulster pack.
Having played in the 2007 Churchill Cup, he is likely to be named in the 'A' squad for the forthcoming games against England Saxons and Scotland 'A' next month.
The Ulster players are currently on a week's leave and will return to HQ for a mini pre-season next Monday before an intensive week with new coach Williams ahead of their next match, against the Newport Gwent Dragons at Ravenhill on Friday, February 15.
With the Heineken Cup campaign now concluded, the end-goal for this season is to stay above Connacht in the Magners League table in order to guarantee Heineken Cup rugby next season.