Well, I think that your accountant is expressing his professional judgement and experience. But, there are some issues I have with his treatment of disallowance of the cell phone expenses.
Perhaps your Accountant should have suggested that in 2007, you ought to have got a separate cell phone that is for your business. In this manner, there would be a justification to write off 100% of your cell phone for business!
Nevertheless, most small business owners generally tend to write off 100% of their cell phone usage anyways. So, taking a 75% business usage appears to be relatively conservative in my opinion.
I think your Accountant appears right regarding your home telephone expenses being generally non-deductible, but I think the disallowance of 100 % of the cell phone expenses is unreasonable!
Clearly, being extremely conservative in itself is not bad, but for disallowing cell phone expenses altogether is really being Unfair to you! You must argue with him a little harder stating the business usage of the cell phone.
If he disagrees with your assertion, then you should consider changing your accountant or getting another CPA to take a look at your personal tax situation, just in case there are other items this CPA has overlooked!