Just thought I would chime in. Right now Palringo and Instango are the two best free multi-IM clients (afaik), and each has strengths and weaknesses. For those reading this thread and trying to decide between the two, let me do a quick rundown.
Palringo Pros:
- Better interface
- Single sign-on (all your IM accounts are tied to your Palringo acct.)
- better support for multimedia im (sound/picture)
Palringo Cons:
- No way to customize the alert, other than with or without a sound notification
- Higher battery drainage (your mileage may vary!)
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Instango Pros:
- Themes
- battery usage optimization (your mileage may vary)
- Alerts for new messages, new messages while Instango is in foreground, and contact coming online, all through the Blackberry's default profile editor
Instango Cons:
- Must select each IM account individually with the BB button and log in one at a time
- Slightly buggy picture message sending (no audio)
Hope that helps a bit.