从逻辑上讲，当固定电话的价格大幅下降时，人们将不再对使用或购买手机感兴趣。市场上对手机的需求下降了，价格也下降了。手机市场将会供不应求。然而，现在使用的手机是智能手机，因此电话定价将不是用户更喜欢固定电话而不是移动电话的唯一原因。在市场经济条件下，商品需求量对人们收入变化的敏感性称为收入弹性。数量变化百分比/收入变化百分比为收入弹性(Deaton & Muellbauer, 1980;cement & Selvanathan, 1994)。富裕国家对粮食需求的收入弹性通常较低，而发展中国家则较高。在发展中国家，由于需要，收入的很大一部分将分配给粮食。食物成为一种强烈的必需品，因此随着收入的增加而表现出高弹性。
在像美国这样的富裕国家，食物是必需品，但也被认为是正常的必需品。作为一种正常商品，它在0到+1之间具有正的收入弹性，而收入增长对粮食需求的影响百分比较小。此外，由于有许多不同种类的食物可供选择，有不同形式的食物定价、食物计划等，收入可能不会对食物需求产生直接影响(McKinnon, 1993)。另一方面，这些富裕国家希望某些商品具有较高的收入弹性。奢侈品的需求收入弹性通常为正。需求的收入弹性大于+1。当收入增加时，需求增加的百分比就会更高(Lazonick, 1993)。有些属于奢侈品的产品被认为是在这种弹性之下的，包括名酒、烈酒和巧克力、豪华旅游和相关服务。所有这些产品和服务在富裕国家都具有高收入弹性。
Logically speaking, when the price of fixed line calls falls sharply, people would no longer be interested in using the mobile phone or buying it. The demand for the mobile phone goes down in the market and so does the price. The market will be short with mobile phones. However, mobile phones being used now are smart phones and hence call pricing will not be the only reason that a user will prefer a fixed line versus a mobile phone. The sensitivity in response in terms of quantity demanded of a good with respect to the change in income of people in the market economy is called income elasticity. Percentage change in quantity/ percentage change in income is the income elasticity (Deaton & Muellbauer, 1980; Cements & Selvanathan, 1994). Income elasticity of demand for food is usually lower in rich countries and higher in developing ones. In developing nations, a high percentage of income will be allotted to foods because of necessity. Foods become a strong necessity and hence exhibit high elasticity with income.
In the case of a rich country such as the United States, food is a necessity but is also considered as a normal necessity. As a normal good, it has positive income elasticity between 0 and +1 and income increase has only a smaller percentage impact on demand for food. Moreover, since many different varieties of food are available, with different forms of food pricing, food plans etc, income might not have a direct impact on the demand for food (McKinnon, 1993). On the other hand, there are some types of goods that these rich countries would expect to have high income elasticity. The income elasticity of demand is usually strongly positive for luxury goods. They have an income elasticity of demand which is greater than +1. When there is an increase in income then there is a higher percentage of increase in the demand (Lazonick, 1993). Some of the products that come under luxury goods and that would be considered to be under this elasticity are that of fine wines, spirits, and chocolates, luxury travelling and related services. All these products and services would have high income elasticity in rich countries.