Cheapest roaming rates for SMS & Data (no voice)

[inquisitor]

I see. Have you considered, that a lot of prepaid SIMs have limited data roaming capabilities? E.g. with all those German eplus-based prepaid SIMs (simyo, blau, solomo) there's is mostly only a single network per country, where data is supported, allthough there's (voice-)roaming for further networks. So if your telemetry device registers on one of the non-datacapable roaming networks it won't be able to establish a data session.