You say that that is the "minimum" price per month ($142.75) but thats if you get the $100/month plan. There is a $60/month plan, that would be the "minimum". Also, if you ad the $20 Value Pack, it INCLUDES 6pm evenings. So really, the minimum would be:
$60 (voice and data) + $20 (value pack) + $6.95 (system access fee) + $0.50 (911 fee) = $87.45 plus tax.
HEY! Would you look at that, that's in the price range which you stated was reasonable.
My point is, it was unjustified for you to state that it would cost a customer $150/month minimum to run an iphone - thats very false as I have proven above.
Maybe you need more daytime minutes, or more data, then yes you will need a bigger plan. Also, i don't know if you are aware but you CAN customize your own iphone plan. For example, if you need alot of voice minutes and not alot of data you can subscribe to a business plan $45/month (for 450 daytime, unlim night and weekends, unlim incoming calls) and add a $30/month data plan (300MB).
None the less, dont get an iphone if you cant afford to maintain it.