If he is more into the Int side then go for the RAF, I would recommend RAF Int Branch as an officer or Int Analyst (C) as a trade.
Only the RAF has a dedicated intelligence branch but few jobs are comms or IT related. The Navy has int jobs filled by officers from non-int branches. The Army has an Int Corps but few jobs are comms or IT related.
Not true. The Intelligence Corps, which handles all aspects of intelligence - Sigint, Humint, Imint etc. There is a dedicated Sigint (comms and IT) role which works in conjuntion with the Royal Signals.
Officer selection for the Army works as follows: go to career office and chat to the people there. They'll assess your husband for offcer selection. They'll send him on a few fam visits to let him see various sides of the Army and he can pick a regiment/corps to sponsor him. Be aware that sponsorship through AOSB and Sandhurst does not garuantee a place in that corps/regiment. He then attends the AOSB to see if he's considered suitable for officer training. If he passes that, he goes to Sandhurst for a year. He must be 29 or under to go to Sandhurst. You may get housing - your husband will be told about that once he's been accepted.
To get into the Intelligence Corps is tough. There is a lot of competition - especially as the Corps is expanding. There are - on average - 5-10 places per intake at Sandhurst and there is no garuantee of getting one. However, if he is suitable and he impresses the selection board, well he has as much chance as anyone.
Once in the Corps, life is pretty varied. There are lots of postings to different types of jobs - mostly around the South of England as well as the chance to work on secondment to various other government departments/agencies. It's a demanding and busy career and promotion can be quicker than in other parts of the Army.