Its really easy to end up with a shrinking taxable revenue base like the Universal Service Fund currently has, causing the tax rate to support lifeline services like what you seek to creep up to impressively high rates: http://www.atconference.com/support/faq/usf.aspx#rates
Lifeline service is a public good, but funding should not come from taxing shrinking telephone bills, but instead from a different revenue source that isn't in the process of notably shrinking every year.
I truly tend to agree with you on this. To complicate matters, I'm pretty sure the Universal service fund not only does things like 911, but also helps poor people afford phone bills. The phone bill tax isn't the best way to do it, I think. Honestly, I think they should be fairly flat easy-to-understand taxes for the phones (including wireless service).
That said, I'm not sure how cell phone taxes wind up looking on a bill, honestly. I have weirdly never had contract telephone service. I've never been able to justify the costs. For years, I had prepaid plans (that kept getting better) in the US, then moved out of the country.
Lifeline service is a public good, but funding should not come from taxing shrinking telephone bills, but instead from a different revenue source that isn't in the process of notably shrinking every year.