[StavrosK]

Can you recommend one that works well? I want one that hopefully provides a Greek DID, I want to be able to make calls from my Android to landlines over my home Internet connection, as you describe, but I haven't managed to find a good (read: cheapish) provider.

[lstamour]

I use voip.ms but many others exist. Anveo, Twilio, Vonage, etc. cheapest might be a service that uses Google, but only for as long as Google offers free calls.

[allannienhuis]

+1 for voip.ms. I've been using them for years - they're inexpensive, lots of features, and service has been great.