Flashing

I'm completely new to this, and I suppose I should read a bit more on it but I was hoping to get some help first before I figure I've made a bad decision haha.

I got a Samsung Juke phone, with a prepay plan with Verizon Wireless. I wanted to switch to Cricket, so I took it down to a Cricket store and they said they'd flash it to Cricket for fifty dollars. One thing they noted was that I likely wouldn't be able to receive picture messages or access the web anymore. I wanted to know if there's another way of flashing my phone that I should look at to get it to work for Cricket that would enable me to receive picture messages. They have my phone now but its possible I can call and cancel.

Also, is there like.. custom software for phones? Like.. I don't know, what all can I... do with my phone when messing with unlocking and firmware and stuff?

Sorry, but help would be appreciated. Thanks.