The line graph illustrates changes in the monthly payment for four different cellular companies in a particular European country from January to September in 2002.
Overall, the prices of all services increased over the period, with the exception of SIM TX, which declined after an initial increase. Although ALPHA started with the lowest price, it saw the most pronounced rise and overtook DOMO by the end of the period.
DOMO consistently offered the most expensive monthly plan throughout the period in question. Although there were some mild fluctuations, it saw a rise from $15 to a peak of $25 in July, before falling modestly to $23 by September. A similar pattern was observed in LEX, which started at about $12, followed by an increase to approximately $18 by the end, with minor dips in February and June.
In contrast, ALPHA provided the cheapest plan at the beginning of the period, at 5$. Its price rose marginally to $8 in April, before dropping back to $5 in June. It was a period after which ALPHA saw the most substantial growth, surpassing all other services and taking the lead with $25 in September.
SIM TX followed a downward trend. Despite experiencing a similar trend as ALPHA between January and April, rising from $9 to $11, SIX TX then diverged in June, when it reached a high of $14. However, this figure then halved by September, marking the only decline trajectory in the chart.