Defaulting on a telephone co. contract?

My sister runs a small company which she recently defaulted on a contract with a telephone co. She had a 3 or 4 year contract and when there is about one year remaining on her existing contract, she cancelled her service and went with another telephone co. provider for a much less monthly bill. She did not sign personal, and signed as a corporate officer with the co. of which she had defulted on. Her small business is still operating, and the previous co. obiously is trying to collect on her. Qestion (1) Is she personally liable in any way, when shed signed as an corporate officer? She said she is a Sub-s corp. Q(2): The collection co. left her a message stating that they are going to persuit this due to she is violating federal law, and public utility issues. Her co. is debt free, and will never obtain any outside credit, my thinking is should she even bother with finding a lawyer since she signed corporately, and it's a small co. with no debt? Any advise?