Hey guys,I started early as you can see

Anyways, I have this chick that i picked up on facebook.This was about last October.We have been talking A LOT on msn,facebook etc but we have NEVER met in real life.Nonetheless she seems into me(calling me sexy,baby,honey etc)
Now i have her number but i've only managed to get 10 mins out of her on the phone before the convo started getting a bit 'cold'.This was about a month ago.Now before you say:'2 mins tops,just grow a pair and ask her out for some lunch',girls at this age kinda have a tendency to love lengthy conversations on phone before going out,(shows substance apparently

)However I can't seem to hack it with girls I've never seen before. Now we txt now and again and there's always a c&f banter being thrown around for good sport.I want to hook up,but exams are nearing so phone is the only way i feel i can escalate the attraction.
So basically I'd be very grateful for any advice to improve my phone game,or any other insight as to how I make sure i don't mess this up.
Thanks.