looks nice, but nokia’s 5110 does not have ir or modem. i think they meant 6110, it has same size and age. but anyway, the cell phone can be controlled via ir (call, hang up, etc. at-commands) and you’ll get sound input&output from phone’s pins (xmic & xear): http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=pinconcel_nokia_5110_6110

Ah – okay. VM == voicemail. So many abbreviations are overloaded these days that people really need to clarify them.

If you’re on the same carrier as the voicemail system, the calls to the VM are free.

Or, wait until the evening. Most plans have “free nights and weekends”.

The major US carriers do some data mining to look for fraud, but none of them do it very well or in real time. The switches that might notice this kind of attack as it is occuring are generally not configured or able (depending on how old the switch is, model, etc) to see that kind of activity, so it is done after the fact from the billing database.
If it were me, I’d assume that eventually the activity will be spotted and the PIN changed (even eve/weekend minutes are detailed in the bill, just not charged). But if you just want existing VMs or want access for a few days and don’t mind leaving a footprint, there you go!