Subject to language in the trust, a trustee is eligible for a "reasonable" fee. This is usually expressed as an hourly rate. In the long run, reasonable is whatever a judge will allow, if a beneficiary sues, or whatever the beneficiaries will put up with. The problem for attorneys is that the prevailing rate for trustees is usually much lower than the prevailing rate for attorneys fees, so if the attorney thinks that being a trustee is the same as practicing law, my guess is the judge would give him or her a haircut, at the very least down to what a professional fiduciary would charge.
You might also look at Probate Code Section 15642(b)(6).