Freedigits and voxalot

[Yazcedric]

Hello, folks,
I have been using voxalot as a gateway for multiple SIP accounts. At home, my ATA is registed to voxalot.
I particularly like its robust dial plan (so that I can choose best rate among different SIP providers depending on the destinations).
I've been using IPKall's DID number, but I am not so impressed by its voice quality. Well, I cannot complain too much because it is free.
I noticed that several members posted freedigits.com's might have better (or reliable?) quality; therefore, I signed up this service.

Here is my trouble;
1) I initially set up to forward calls to sip:XXXXXX(my voxalot #)@us.voxalot.com in Freedigits.com's dashboard (ie my account page).
After that, I set my voxalot to forward incoming calls to voipcheap.com account as a default, which dials out my cell phone.
When I call my Freedigits.com's DID, there is a brief calling tone (~5sec), followed by a message "the number XXX-XXX-XXXX (my freedigits' DID) is on the phone" and voicemail kicks in.
I tested my IPKall's DID number which is currently set to forward calls to voipcheap.com (and dial-out the same cellphone as above) and the call went through - so I don't think voipcheap.com -> cellphone is the cause.

2) Then, I registered freedigits.net as one of my providers in the voxalot account.
Using proxy.freedigits.net as domain and DID number (excluding 1) as account number/username on my account page, freedigits.net was successfully registered.
However, when I dialed freedigits' number from PSTN (not voip phone), the call goes into the voicemail.

I am not sure whether my setting is not correct or I should give more time to update these changes.

Actually, my goal is as follows:
when I travel outside of USA, I would like to receive calls on the cellphone (prepaid cellphone in UK, for example).
But, I do not want my callers to pay international rate to dial UK cellphone number.
Since some VoIP providers (such as voipcheap.com) have relatively reasonable rate to call-out (or call-forward) to UK cellphones,
I would like to make a link
US DID number -> Voxalot (call-forward) -> registered (in Voxalot) voip provider -> cellphone in Europe

Or, should I just simplify my setting such as
US DID number -> voip provider -> cellphone in Europe?

I may expect too much for current voip technology, but I would appreciate if you can tell me why my freedigits incoming call does not go through to voxalot.
Particularly, I am wondering why it gives me "the number XXX... is on the phone" message.

Yazcedric