If you subscribe to Digi, you can apply for D'Campus where you can make free calls after RM1 of usage per day. It's really popular with students there.

Bringing your guitar should be fine. Acoustic or electric guitar?
One big warning though: Most of UTM's drains are uncovered, some are quite deep and extremely dangerous to newbies. I saw a person fall into a waist-deep drain right outside the hall during MHS (Minggu Haluan Siswa or Orientation Week) and several others tripped and fell on the way back to the hostel. There are no guardrails as well, one slip might send you tumbling down into the river. So bring along a torchlight or handphone with torchlight functions in case the road lamps aren't functioning and the roads are pitch-black.
Items which will be provided for you by UTM: Metal cupboard with mirror, desk with chair, metal bed frame, mattress, window curtains. If you're lucky you might end up staying alone in a double room.
Some items that you might need to bring yourself: Pillow (and/or bolster), bed sheets, locks for your cupboard. You can bring electrical equipment such as kettles but rice cookers are not allowed. You need to register your handphone charger as well as laptop at the kolej office (for free) or else they'll issue a summons. Stalls should be open on the first day of MHS and you can get your essential items there. Shuttle buses to Jusco in Taman Universiti are available during the weekends (after class starts).
Some items that you might need during MHS: Small bar of soap, fork and spoon, bandage, torchlight, cap, small umbrella, 2 or 3 sets of formal clothing and a pair of sport shoes since Sports Day might be held on the last day of MHS. I brought along a novel and mp3 player.
Life during MHS can be as tough as heck, since everything is meticulously planned out for you newbies from dawn to dusk. It's organised by agents from the MPP (Majlis Perwakilan Pelajar or Student Representative Council) and food will be supplied by them four times a day (breakfast, lunch, dinner and supper). Technically you
can skip certain parts and sleep in on certain days but it's not recommended, since the bulk of information provided will be during MHS. You'll get your Matrix Card by the end of day 1 and register for your subjects in the middle of the week.
Since I won't participate in being an agent for MHS, I'm here to answer any questions until the new semester begins.

i highly recommend AGAINST bringing anything valuable such as laptops during MHS. most of the time it'll be left in ur room. assuming they did not change the locks and the last year's students made an illegal copy of the keys, they might have access to ur room.
if u have a locker, use it. if u have ur own padlock, even better.