Just because it is on the MLS does not mean that it will ever appear on Trulia. The listing must be "fed" by you agent to Tulia or, fed trough syndication utilizing any number of sites already feeding to Trulia. Postlets.com is just one of them. The agent must manually enter the data to another site or, create a feed which is then uploaded to Trulia directly. Again, this is an additional step that must be done in addition to simple entry on the MLS.