Almost all DOCs and the BOP will block a call forwarding number no matter where it is from . The do this for very real security reasons. I do not think any of these services can actually offer what they promise . If your PP is in a system where they have can either pay for a call from their account or use a "phonecard " they might be able to call a cell phone only if they pay for the call .
Other than that you need a land line and often have to submit a phone bill to the DOC/BOP Some now do allow a call to a cell phone only after seeing actual bill . I think it will slowly change as more peoples primary phones are cellphones
Peanut is right in many prisons especially max security places you have to be on a visitor list and approved to get a call