vACC Slovenia covers virtual airspace over the Republic of Slovenia with the following facilities:

Name Callsign Frequency(MHz)
Ljubljana tower LJLJ_TWR 118,000
Ljubljana approach/departure (heavy traffic) LJLJ_APP 118,750
Ljubljana radar LJLA_CTR 135,270
Maribor approach/departure LJMB_APP 119,200
Portoroz/Portorose tower/approach LJPZ_TWR 129,320

Usually You'll see LJLA_CTR available (Ljubljana radar) which will handle also take-offs and landings on all Slovenian airports if there are no TWR or APP facilities online. The exception is in MUREG sector, which is west of Pohorje hill (the border is around the line from GRZ VOR to ZAG VOR) which is usually handled by LOVV_CTR at FL150 or above. 
Transition altitude in Slovenia is currently 10500 ft, transition layer is set by ATC, usually FL100 or FL110 depending on the pressure.

For flights from Slovenia to surrounding countries, the ATC will handoff You to appropriate frequency but nevertheless here is the table for most common handoffs:

Country Name Callsign Frequency(MHz)

Croatia

 Zagreb center LDZO_CTR 135,800
Zagreb approach LDZA_APP 120,700
  Pula approach LDPL_APP 124,000
  Rijeka approach LDRI_APP 119,000

Austria

 Wien center LOVV_CTR 134,3500
  Klagenfurt approach LOWK_APP  
  Graz approach LOWG_APP  

Italy

 Padova radar LIPP_CTR 133,700
Milano radar LIMM_CTR 127,450
  Venezia approach LIMZ_APP 118,900
  Ronchi approach LIPQ_APP  

Hungary

Budapest center LHBP_CTR 133,200

Due to the lack of ATC staff in Slovenia, LJLA_CTR is currently working over the weekend, i.e. on Friday, Saturday and Sunday from 21:00 hrs local time (19:00 UTC) till at least 23:30hrs local time (21:30 UTC). If You need ATC for other days, just send as e-mail!

Every newbies form Slovenia interested in virtual flying, we recommend joining to our organization. Membership is free but You get aid in training, You'll get informed about news, events and so on. Just fill in this form.