well if your phone is locked, then it just means your phone can only accept a specific carrier's sim card. for example, if your phone is locked to vodafone, then you can only use the vodafone network.

if you flash your firmware, then it erases everything in your internal memory. so any contacts, games, apps, etc will be gone.

if your phone is locked to a carrier, you can still upload swf files! you just can't use another carrier.