Why am I notified about some missed calls via a text from +8888?
5 seconds with google showed me this: http://forums.crackberry.com/blackberry-pearl-flip-f85/rogers-sends-8888-text-message-every-time-someone-calls-332862/ 

Seems to be a "service" Rogers offers where they notify you if you miss a call. You need to call their customer support line and ask them to disable the "Whocalled" service on your contract.