Hi Jo,
All ATMs of the BNI Bank accept both Mastercard and Visa. You can find their branches and match them up to your route at [http://www.bni.mg/pdf/Carte_reseau.pdf]
BFV-Société Générale now claim on their website at [http://www.bfvsg.mg/agences_province.html] that you can use both Mastercard and Visa.
You’ll be better off making your withdrawals at BNI, as they allow you to withdraw 400 000 ariary per transaction (if the ATM has enough cash left in it), while BFV-SG allows you only 300 000.
Both allow you multiple transactions up to whatever limit is imposed by your card issuer.
I see that you’re UK-based. Many British banks issue a Visa debit card with a current account. If you have one of these, take it to Madagascar. They work perfectly well in the ATMs there, and the transaction charges raised by the bank for a cash withdrawal are usually much, much lower than for a credit card.
Vodafone is not present in Madagascar – you’d need to check who their roaming partner is, but roaming in Madagascar is generally very expensive. If your mobile doesn’t have a SIM lock, then bring it with you and buy a SIM card (“une puce”) of one of the local providers (Airtel, Orange Telma). These are very cheap, they operate on a pre-paid basis, and SMS to Europe are inexpensive. If your phone is simlocked, you can get yourself a basic phone for very little money in Madagascar.
Up to now, I’ve only found Wi-Fi in the larger towns and cities (Tana, Tamatave, Toliara, Mahajanga, Diego...). I haven’t stayed in any of the hotels you list, but I’ve stayed in others at some of the places you mention and they didn’t have Wi-Fi.
