IPhone 3gs Why upgrade or add line

The 3G will get MMS later this summer and tethering will be added for an additional fee later on. If you need video recording or a compass then you might be interested in the 3G S.
The only other major GSM network in the US is T-Mobile and their coverage in many places is much weaker than ATT.
MacBook , Mini, Airport Express, iPhone 3G x 2 Mac OS X (10.5.5)

There are some serious hardware improvements in the 3GS that are worthy of a look before deciding. Faster CPU and double the RAM.
iMac MacBook iPhone Mac OS X (10.5.6)

My primary reason for upgrading is the 32GB storage capacity, my 8GB 3G is always full. I would also like a little quicker performance.
I do want tethering (the sooner the better), but I dont care about MMS. Video and a better camera might be fun, but not a good reason for me to upgrade. Voice controls sound interesting, but I usually end up shutting them off if they dont work perfectly.
I could live without the upgrade, but my daughter really wants my 3G so Ill probably do it.
MacBook Pro, Powerbook, Mini, iphone, ipod Touch, Apple TV, etc. Mac OS X (10.5.6)