tether not working with Voila Haiti

Any suggestions on how to get Tether working with this provider?

Have Blackberry Curve 8520, tied to provider Voila in Haiti.
EDGE works fine on the Blackberry.

Have Tether trial installed on Blackberry and on WinXP laptop, version 1.4.3.7.
Have also tried later version of Tether, but same problem:
No connection is made with APN settings on Blackberry not checked (manual entry disabled)
No connection is made with the standard APN settings for the provider (intenet.voila.ht)
Connection is made with APN set to Blackberry.net:9201, packets sent but no packets received.

Tether connects to Blackberry via USB. Tether window on computer shows packets sent but none received. Data sent and packets sent count upwards, but data received and packets received remain at 0. Status: Connected to Blackberry.

On Blackberry, Tether application shows x.yk packets sent up, 0 down, Status: Tether is running

Blackberry setup as follows:
Options -> Advanced Options -> TCPIP
APN Settings enabled
APN Blackberry.net:9201
APN Authentication not enabled

If APN setting on TCPIP menu changed to: internet.voila.ht (APN found on other forums),
no connection at all is made,
Status message shown on Blackberry: Failed to Find an available port

If APN settings not enabled on TCPIP menu, no connection at all is made,
Status message shown on Blackberry: Failed to Find an available port

Options -> Advanced Options -> Host Routing Table
GPRS HT (372) (37200130)
detail:....APN: blackberry.net, IP/Ports: 206.51.26.192:19815:19814, Load Sharing Byte: 0

Options -> Mobile Network: Data services On, Mobilie Network Voila.
Result of Diagnostics Application on the marked network:
...Radio Access: Edge, Network: COMCEL, IP Address: 10.64.223.xxx (subsitituted the last octet with xxx just in case Voila administrator is reading this)
Blackberry Registration: yes
Connected to Blackberry: Yes
Blackberry PIN-PIN: yes ....

Suggestions?

Thanks!