Also TxCall1 and TxCall2. It really depends and is generally regional in nature. Some regions use their regional Trunked systems some regions use VHF Interop, etc. etc.
Yes. Law is 154.950 and Fire is 154.250, both simplex. These are known as "Statewide Mutual Aid" channels, and are usually tagged as TXLAW 1 and TXFIRE 1, respectively.
154.250 is not a statewide fire frequency in Texas.
Any agency that still has channels labled TXLAW1, TXFIRE1, etc. is incompetent. They should have been changed before Jan 1, 2013.
For all Texas conventional interoperability frequencies, information and document links see Common/Shared (TX) - The RadioReference Wiki