Shape Services just added Skype chat to their popular IM app earlier in the month and now they have added Twitter support. Pretty cool stuff if you use their client. I personally use the RIM clients for free but I even have a friend who uses IM+ simply to get IM without a BlackBerry data plan.
You can download the public Beta of IM+ for BlackBerry with Twitter features at the links below. If you do not already own a copy of IM+ you can pick one up in the store currently for a pricey $39.99.
Here are the links: