You're going to spend how much per month on smartphone plans and you're worried about $50 on the initial phone price?
Think about it: even if you use a minimal $50 smartphone plan, per person that's $1,800 over three years. You'll probably keep that phone for most if not all of that period, and of course two lines could boost that up to $3,600. Dropping an extra $50 for each iPhone 3GS over a Bold 9700 is trivial if it means you'll be happier with your phone over its useful lifespan.
As long as those friends aren't explicitly depending on BlackBerry Messenger -- if it's just regular AIM/MSN/Yahoo or SMS/MMS, that's fine -- you'll probably like an iPhone a lot. The touchscreen keyboard takes a little while to learn but can actually be faster than the Bold's (I've used both), especially if you need to cut and paste text or insert numbers and special characters.
There's already a Sirius iPhone app, of course, and more importantly the iPhone is worlds better as a media player. RIM does have a BlackBerry media syncing app, but there's nothing quite like directly syncing with iTunes.
One last bit: no matter which phone you get, don't expect the battery life you're used to with a "regular" phone. I'd give a slight edge to the Bold for battery, but having background e-mail checks, active web browsing and music will use more battery than something that only ever gets pulled out to make a phone call or text message. Battery to me isn't an issue as long as you remember to connect the phone to your computer at night; with an iPhone, you'd want to do that anyways to back up data and sync any new apps, music or photos.