My phone rings a lot during the day and since I'm in Europe, I'd be pretty upset to get calls in the evening / at night from random sponsors.
E-mail, ICQ. Don't fucking call me unless you want to let me know you just wired a shitload of money and wanted to make sure I got it
Also OP: If you feel need something, just contact the sponsor on ICQ. Works for me and most rep's I've worked with have been friendly and helpful (thanks!).