Below is a quote from an email I received from RIM on Friday regarding this issue:
"Today I tested 3rd party app push on bundle 178 (18.104.22.168). This proved to be successful in receiving 3rd party applications wirelessly from my BlackBerry Enterprise Serer. I also tested pushing Multiparty talk and it was successful.
Orange UK accepted this build and now have it posted on their website for download.
I haven't tested it myself yet, but it looks promising. I will post my findings later on Monday.