Yeah, tethering is not really a viable option on the 7520, the 7100i if it was in a WiDen coverage area may be tolerable, but not enjoyable.
I was/am on the Unlimited plan, so for $127 a month after corp discount, I get unlimited airtime, period. No overages, ever.. It was a pretty sweet plan and I wish I could keep it with me when I move to the 8800.
I hated that SMS issue, but when the 7100 launched, they launched MMS messaging for the 7520 as well and I paid the $5 a month for it, and that let me send and recieve SMS/MMS messages with no fuss and then I could tell who they were coming from.
Verizon definatly has the better network, I think the fact they're in the lower spectrucm helps them out. (850 vs 1900). I actually bought a repeater for the house for the 1900mhz band (T-Mobile user in the house as well) and it worked VERY well to get the Sprint service useable in the house. Not 5 bars everywhere in the house, but places where I would drop calls, I could now hold 1-2 bars.. Not bad for under $200.
Long story short, I'm going back to my 7520 right now based just on the call handling abilities, I'll keep putzing along on a slow blackberry and then deal with my EVDO wireless card for the laptop (Easier anyways and then I can talk and surf)
You'll really love the 8703e when 4.2 drops for it and you'll have bluetooth tethering. =)