550D Wireless flash
Sorry but not possible. Only built in wireless on the 7d/60d/t3i(600d)
You need the 580 ex(II) or st-e2.
Another option is radio triggers or extension cord.
Or the YongNuo ST-E2, which is less expensive and apparently better in some ways than the Canon equivalent.
Check out the unofficial Rebel forum FAQ - http://snipurl.com/RebelFAQ