provider may only allow incoming data calls to subscribers that have a
special ‘data subscription’, which comes with a special second phone
number to call in order to reach the CryptoPhone in encrypted mode.
If your local GSM provider and/or call plan requires such an additional
data subcription, you need to order this service from your local GSM
provider. If you are assigned a second ‘data’ phone number, always call
this number when making an encrypted call.
[Improper Signalling]
Some providers may not recognize that a number
you are calling in encrypted mode is a digital GSM data number, and
may erroneously try to handle the data call via an analog modem. In
this case, incoming calls may erroneously be signalled as analog unen-
crypted voice calls, and consequently they can not be picked up in Cryp-
toPhone mode. This issue can be recognized by the called party when
a modem tone can be heared after picking up the phone. If switching
the line type to V.110 is not possible or does not solve the problem, you
will either need to get a separate data number as described above, or
you may need to switch providers. Very few GSM service providers also
may not pass data calls to some or all other providers. If your GSM ser-
vice provider does not offer cross-network data calls, then encrypted
calls are only possible within the same GSM network.
