sql query each hour of a day and results in 1 column

I'm new to informix and I'm using it because we use cisco uccx and we need to run detailed reports for our call center to get better statistics. My superiors want a report that will get me the number of calls each hour so that over time we can see what times of days and days of weeks are the busiest. The query I have now:

select COUNT(*)
from ContactCallDetail
where contactType=1 and startDateTime > '2013-07-17 15:00:00' and startDateTime < '2013-07-17 16:00:00';

works good for one given hour. I would like to be able to do this for about a 11 hours period but not sure how to go about the query. I'm thinking the count would be in 1 column and each row would be an hour of the day and how the count of calls. does anyone have any suggestions on how I can go about this? I really appreciate any help.

Thank You