E-Mail or other interface? MMS are relatively expensive for many people I know (nobody uses them and therefore nobody cares when selecting a phone plan what they cost, vs. people with a smartphone nearly always have data plans)
+1. An additional interface would be great. Looked at doing something similar a while back and quickly realized I would need multiple endpoints. One endpoint would be for trusted users who could automatically add to the stream, while a 2nd endpoint would require manual approvals. It would help prevent awkward moments when friends decide to have "fun" after a couple drinks.