I am switching from inactive to 25B in the Reserves. What can I expect switching to Reserves?

Your experiences in the Army Reserve will depend on the unit you are joining and what part of the training cycle, called Army Force Generation (ARFORGEN).
Expect to spend most of your time with the S1, inprocessing to the Army Reserve and obtaining guidance from your Signal section chief as you are starting as a 25B.
In the reserve, you need to take the initiative and keep in touch with your section leaders and 1SG, even a simple phone call between battle assembly will set you apart from the people who just hang out.
You will be issued some gear by your reserve unit and when you mobilize for an overseas tour you will receive a full issue of body armor and combat vests with appropriate accouterments.
Regarding AIT, I think you will find Fort Gordon, GA a nice post with the classrooms and facilities centrally located.
I strongly recommend you pay attention and do well and work yourself into SSG positions and then strongly consider cyber, warrant officer or other technical positions as you find your interests in the Signal Branch.
God Speed in your journey.

Youll be in with the reclassers... I reclassed in 02, and it was interesting. Had a PVT from my class come up and ask where the mail room was.. I pointed a direction, told him how many doors to go down in the next building.. and he was good to go. Immediately after, I had a SGM come give me a talking to because I was an NCO giving directions to a private without a battle buddy...

You will most likely be working i an S6 help desk assisting customers with basic computer trouble shooting software and hardware and in the field you will be setting up and maintaining the cpn and stt.