You can subscribe via SMS or USSD code:
Subscribe by SMS
SMS 101 to 2525.
SMSs sent from a prepaid subscriber to 2525 are free.
Each SMS from a postpaid subscriber to 2525 costs 0.01 AZN.
Subscribe by USSD Code
Dial *100*101#YES on your phone.
Please SMS balans to 2525 or dial *100#YES on your device to access balance information.
Each SMS to 2525 costs 0.01 AZN.
Usage of free Whatsapp texting is suspended the moment the allocated data within Roaming Internet Pack has spent.
If roaming internet pack is not renewed, standard tarif rates will be applied.
You can see the full list of countries here.