campyracr, How are you dialing in? Are you having someone manually transfer you to *10? Are you dialing in a DID number that's part of an incoming T-1? Are you dialing in a single loop-start remote access line that has its own phone number?
In the past I had sporadic dial-in problems connecting with single loop-start remote access lines. If there was a lost session I couldn't reconnect. Just dialing the phone number from a cell phone would result in nothing picking up or a fast busy. I had to resort to physically going there and resetting the loop-start port in question at an operator phone or directly connected using WinSPM.
If you are getting transferred in from a user physically on-site then there might be pilot error. If there are consistent issues past pilot error then resetting the internal modem might be something to try. Less disruptive than restart the whole phone system if it's during business hours.
If you are coming in through a T-1 with some sort of DID assignment then perhaps there's an issue where the call isn't routing in correctly.
All of these are just educated guesses. But without resetting the internal modem or loop-start ports or checking DID assignments it's hard telling. There are a lot of possiblities.
One possibility I forgot to mention is that if you are dialing in through loop-start remote access lines there is specific timing that needs to happen between WinSPM dialing the phone number, waiting a number of seconds, then dialing the barrier code, then dialing the *10. As an example, an external connect string could be ATDT 5551212,,,,,,1234,*10 in order to dial the 5551212 phone number, wait awhile, enter the 1234 barrier code, wait a short while, then dial the *10.
Just a few suggestions of things to look at.